METABOLISM OF AMINO ACIDS

REVIEW

ARTICLE

117

PESrmzcs, January 1958

METABOLISM

OF

AMINO

ACIDS

A

Review

By Selma E. Snyderman, M.D.

Department of Pediatrics, New York University-Bellevue Medical Center

T

subject of metabolism of amino acids

may be of special interest to the

pediatri-cian. The requirement for protein during

infancy and childhood is higher than at any

other time of life. Not only is protein

re-quired for the replacement of tissue which

is being constantly catabolized but an

cx-cess is needed for the process of growth. A

definition of the requirements for protein

must include both the quantity and quality

of the protein. In turn, the quality of a

pro-tein is directly dependent on its composition of amino acids.

Amino acids are important for metabolic

purposes other than supplying the

consti-tuents of tissue protein. Phenylalanine, for example, may be converted into tyrosine

and then enter into the channels of protein

formation, or may enter into the synthesis

of thyroxine and epinephrine or into the

formation of melanin. Tryptophan, in

ad-dition to being an essential amino acid for

synthesis of protein, is a direct precursor of

nicotinamide and of serotonin. Hence, a

knowledge of the requirements of the

in-fant for amino acids in both health and

disease is of fundamental importance in the

nutrition of the infant and child.

Secondly, there are a number of

aberra-tions in metabolism of amino acids that are

manifested during the pediatric years.

These may be subdivided into congenital

and acquired metabolic abnormalities. It is

quite possible, too, that there are still

un-recognized syndromes that are caused by or

are closely related to abnormalities of

me-tabolism of amino acids.

ADDRESS: 550 First Avenue, New York 16, New York.

INTERMEDIARY

METABOLISM

The principal source of amino acids is

the enzymatic breakdown of dietary protein

in the gastrointestinal tract. The greater

ab-sorption takes place in the upper

gastroin-testinal tract :‘ amino acids are absorbed

both by diffusion and by an active

trans-port mechanism. There appears to be active

uptake of amino acids by gastrointestinal

mucosal cells, since feeding labelled

com-pounds results in an accumulation of

Ia-belled compounds in these cells.2 An

up-take of L-amino acids by the intestine of

the rat against a concentration gradient

also suggests that there is active transport.3

The mechanism of transport is specific for

the L-isomer.4 The in-vivo absorption of

certain amino acids may be inhibited by the

presence of others. Thus, L-tryptophan

decreases the absorption of histidine in the

rat,5 and leucine interferes with the

absorp-tion of both phenylalanine and isoleucine.#{176}

From the gastrointestinal tract, amino acids

are transported via the portal tircu1ation to

a state of equilibrium with the various

tis-sues.

The complex processes of synthesis of

proteins from amino acids cannot be

sep-arated from the processes of tissue

catabo-lism. A continuous turnover of protein and

hence of amino acids is constantly taking

place in the body. Even in the adult animal

in nitrogen balance there is a continuous

breakdown and synthesis:

ProteinAmino AcidCathbolic Products

This concept of the dynamic state of body

Schoen-118 AMINO ACIDS

heimer, Rittenberg and their associates7’#{176}

who used N15-labelled amino acids. When

N’5-labelled amino acids or ammonia were

fed to rats, the isotope was later found in

all but one (lysine) of the amino acids of

the tissue. The amino acid fed had the

highest concentration of N15 followed by

glutamic and aspartic acids. The finding of

high concentrations of the isotope in these

amino acids is in accord with the knowledge

that these amino acids undergo rapid

trans-amination.

The major initial reaction in the

catabo-lism of amino acids is the loss of the alpha

amino group. Either oxidation or

transam-ination may bring about this deamination.

The 8 of alpha amino acids

results in the production of the

correspond-ing alpha keto-acid. The keto acid may be

reaminated and incorporated into protein

or may be degraded to yield, ultimately,

water and carbon dioxide. It has been

shown that certain amino acids increase

the formation of glycogen or glucose in the

liver while others take part in production

of acetic, acetoacetic or l-hydroxybutyric

acid. Thus the further metabolic fate of

their derived compounds is closely linked

to metabolism of carbohydrate and fat.

Oxidation of amino acids is accomplished

by oxidases which are present in the largest quantity in the liver and kidneys and re-quire flavoproteins as coenzymes.’9 These

oxidases are highly specific. Oxidation

pro-cedes as follows:

RCHCOOH+O2-RCCOOH+H2O2

NH

RCCOOH+H2O-RCCOOH+NH,

NH

The end products are the corresponding

alpha-keto acid and ammonia. An alternate

pathway for amino acid catabolism is

de-carboxylation.2#{176} This is the splitting off of

carbon dioxide with the formation of a

highly active amine:

RCHCOOH-RCH2NH2+CO.,

NH,

All the enzymes which produce this

reac-tion, except for histidine decarboxylase, re-quire the presence of pyridoxal-phosphate as a coenzyme. Decarboxylation reactions

are of significance in the formation of such

compounds as taurine from cysteic acid,

his-tamine from histidine, and serotonin from

tryptophan.

Transamination” is probably one of the

most important reactions in the

intermedi-ary metabolism of amino acids. This form

of deaminization occurs as the result of the

transfer of the amino group of an amino

acid to its alpha keto analogue. Although it

was first believed that transamination was

sharply limited to a certain few amino acids,

it has been recently shown that these

reac-tions involve practically all amino acids.”

The occurrence of glutamate-aspartate and

glutamate-alanine reactions were among

the first to be demonstrated. They are as

follows:

aspartate+alpha-ketoglutarate!=oxaloacetate+gluta-mate

gluthmate+pyruvat&=alpha-ketoglutarate+alanine

Vitamin B62’ is intimately concerned in

transamination reactions; it has been

sug-gested that an interconversion between the

aldehyde (pyridoxal phosphate) and the

amine form (pyridoxamine phosphate) are

involved in the mechanism of

transamina-tion. Transaminase activity is widely

dis-tributed in the tissues of higher animals.

The processes of catabolism and

anabo-lism of protein result in the irreversible

de-struction of some of the amino acids. The

amino groups liberated by deaminization

processes can be used in transamination.

However, many of them enter the metabolic

channels of formation of urea. Formation of

urea occurs in three main phases. The

amino groups are transferred to ornithine

which simultaneously takes up carbon

di-oxide and water to form citrulline.’4

Citrul-line receives another amino group from

as-partic acid by transamination to become

arginine.’5 In the third phase, arginase

splits arginine into urea and ornithine. Urea

is excreted via the urine, and ornithine once

diagram is a simplified version of the proc-esses of urea formation.

Carbamyl

+ Carbamyl-aspartic acid

+

Aspartic acids Ornithine

Ar

nine Citrulline

Urea

+ Argino succinic acid

Aa’

\\

I,

Oxaloacetic acid

Malic acid

Fumaric acid

A small amount of ammonia is also usually

excreted. The source is blood glutamine;

ammonia is liberated from it enzymatically

in the kidney. A small amount of the

in-gested amino acids are excreted in the

urine as such. This usually amounts to

be-tween 1 and 2% of the dietary intake.’6

This section on intermediary metabolism

of amino acids has purposely concerned

it-self only with the general metabolic

pm-ciples. Theme is a voluminous literature2? of

the detailed metabolism of each individual

amino acid which is beyond the scope of

this paper.

DETERMINATION

There are a number of methods available

for the determination of amino acids. These

include chemical, microbiologic, enzymatic

decarboxylation, isotope dilution, and

chro-matographic methods. The chemical

meth-ods, with a few exceptions, are quite

in-volved and not very accurate.

Microbiologic determinations make use

of various lactic acid bacteria.28 These

bac-temia require a number of amino acids for

maximum growth; when one of these is

omitted from the medium, growth fails.

When the amino acid is restored, growth

occurs in proportion to the amount

sup-plied. This method is quite accurate and

can be performed on small amounts of

ma-terial. Its disadvantages are that there may

be changes in the requirements of the

or-ganism, the requirement of each organism

for each amino acid is not absolute, and the

materials being analyzed may contain

in-hibitors.

The method of enzymatic

decarboxyla-tion’9 makes use of an enzyme system that

has the property of specifically

decarboxy-lating one amino acid. The carbon dioxide

that is thus liberated is measured by

stand-ard techniques. These methods are rapid

and accurate. However, the enzymes may

be very difficult to prepare and occasionally

do not give standard and reproducible

re-sults.

The isotope dilution method3#{176} has had

recent limited use. If a known amount of

an amino acid labelled with N1’ is added

to an unknown mixture, and then the same

amino acid is isolated, a determination of

the concentration of the isotope will give

a direct measure of the amount of the

amino acid present in the unknown mixture.

The reduction in the concentration of the

labelled element present in the added

amino acid indicates to what extent the

labelled amino acid has b#{231}endiluted. A

mass-spectrograph is necessaty for the

meas-urement of the N’5; these sfruments are

not generally ‘ailable.

Chromatography has recen.1y been

wide-ly applied to amino acid determinations.

Paper chromatography which was first

ap-plied to the determination of amino acids

in biologic material by Dent,” is technically

an easy procedure and gives rapid and

re-producible result of a semiquantitative

na-ture. Separation of the amino acids takes

place because of the relative solubilities of

each acid between the water held in the

fibers of the filterpaper and a solvent not

miscible with water, which is allowed to

creep along the filter paper past the spot

which contains the material to be assayed.

deli-120 AMINO ACIDS

nite speeds, arrange themselves in a

char-acteristic order, and they can be identified

after development of color with ninhydrin.

Column chromatography has the

advan-tage of being highly quantitative. An ion

exchange resin is used in the column,” and

the amino acids are eluted by the use of

buffers ranging from pH 3.4 to 11. As little

as 3 to 6 mg of a mixture of amino acids

can be assayed and recoveries are 100 ± 2%

for the majority of the amino acids.

Excep-tions are the basic amino acids which give

lower yields. The procedure is not adversely

affected by the presence of inorganic salts;

hence preliminary desalting procedures are

not necessary in assays of blood and urine.

The only disadvantage is that the procedure

is quite time consuming and also requires

special equipment. Moore and Stein” have

recently modified this method by changing

the type of resin. This has the added

advan-tages of improving the resolving power,

per-mitting the determination of peptides on

the same column as the amino acids, and

of hastening the procedure.

FREE AMINO

ACID CONTENT OF

PLASMA

The alpha-amino nitrogen content of

plasma during childhood is in the same

range as that of adults. Woodruff and

Mann34 found that the normal adult range

was 3.37 to 4.23 mg/100 ml while Lyttle

et al.” found it to be 2.92 to 4.63 mg/100 ml

in normal children. There has not been any

systematic investigation into the content of

amino nitrogen in the plasma during the

newborn period and infancy.

Thus far, there have only been two

re-637 on the concentration of the

mdi-vidual amino acids in the plasma

deter-mined by column chromatography. Tab1e I

summarizes these values. There does not

seem to be any significant variation in

con-centration of amino acids in the plasma

with age. Huisman, however, does record

two as yet unidentified peaks in his assays

in children less than 1 year of age which

were present in very small quantities in the

plasma of a 5-year-old child and never seen

in adult blood. Similar determinations have

not as yet been performed on blood

sam-ples of premature and full-term infants.

However, Woolf et al.,2 using paper

chro-matography, found a much higher

concen-tration of lysine in the plasma during the

newborn period and also small amounts of

ethanolamine and hydroxyproline which

they did not find in normal blood of sub-jects of other ages.

Of special note in the analysis of amino

acids of plasma are the very low

concen-trations of glutamic and aspartic acids.

These substances are present in the amide

form. Plasma differs in this respect from

most other tissues where these amino acids

are found in high concentrations.

There are some differences between the

amino acid patterns of plasma and urine.

In most urines, taurine is a major

compo-nent (except during the first year of life)

while concentrations of proline and valine

are low; more glycine is present than

ala-nine and there is more histidine,

1-methyl-histidine, and 3-methylhistidine than lysine.

The situation is just the opposite with

re-spect to the distribution of amino acids in

plasma.

The content of amino acids in plasma

is kept fairly constant#{176} and increases rela-tively little even after a large meal of

pro-t&n. This increase may be about

40%

the fasting level. There are no significant

quantities of peptides in venous plasma

either in the fasting state or after a protein meal.

There has been one determination of the

amino acid composition of blood cells using

column chromatography. There was a

greater concentration of glutathione,

tau-mine, glycine, omnithine, aspartic and

glu-tamic acids and a lower concentration of

valine and cystine than is present in plasma.

The concentration of the remaining amino

acids in the cells and plasma was similar.

THE AMINO ACID COMPOSITION OF

OTHER TISSUES AND BODY FLUIDS

The composition of other human tissues

is similar to that of plasma except for a

much higher content of glutamic and

con-TABLE I

CONCENTRATION OF FREE AMINO ACIDS IN PLASMA

(mg/100 ml)

Average of

S Adults*

Average of

2 Adultst

1-year oldt

5-year oldt

2-month-old**

Asparticacid 0.03 0.18 0.1 0.15 0.14

Glutamic acid 0.70 0.95 1.5 0.85 1.5

Asparagine and glutamine 8.88 4.36

Glycine 1.54 1.6 . 1.0 1.85 1.56

Alanine 3.41 2.2 1.8,5 3.7 .6

Aminobutyric acid 0.30 0.1

Valine 2.88 2.5 0.5 3.5 1.47

Leucine 1.69 1.6 0.65 2.25 1.05

Isoleucine 0.89 0.7 0.15 1.4 0.57

Serine 1.12 1.56

Threonine 1.39 0.9 1.2 1.5 1.61

Cysteine and cystine I.18 0. 95 0.84

Methionine 0. 38 0.4 0.6

Taurine 0.55 0.62 0.2 0.85 2.13

Proline .36 1.6 1.2 2.1 1.8

Phenylalanine 0.84 0.8 .0 1.8 0.87

Tyrosine 1.03 1.2 1.35 1.75 1.27

Tryptophan 1.11 3.2 1.75 0.8

Histidine 1.15 2.4 1.7 1.35 0.71

1-Methylhistidine 0.11 0.30

3-Methylhistidine 0.08

Ornithine 0.72 0.52

Lysine 2.72 1.45 1.55 2.4 1.34

Arginine 1.51 1.5 1.55 0.4 0.70

Citrulline 0.50 0.45 0.2 0.75

9-alanine 0.25 0.2 0.2

* Stein and Moore. t Huisman.’7 ** Westall et38

tains a large amount of citmulline; this amino

acid is usually present in only very small

amounts in other biologic materials.

Cere-brospinal fluid has a much smaller content

of all the amino acids with the exception of

glutamine, which appears in large

quanti-ties.

The intracellular concentration of amino

nitrogen is much greater than the

extra-cellular concentration.41

URINARY EXCRETION OF AMINO ACIDS

In 1911, Simon42 first observed that the

excretion of alpha amino nitrogen of young

infants is much greater than that of adults.

If the amount of alpha amino nitrogen is

expressed as the percentage of the total

quantity of nitrogen in the urine (amino

acid coefficient) a figure as high as 10% may

be obtained in the newborn period while

the highest figure in adults is 2%. Child,43

who used the very accurate method of Van

Slyke to determine the content of alpha

amino nitrogen, found that children

cx-creted 2.2 mg/kg/day while premature and

full-term newborn infants excreted an aver-age of 8.6 mg/kg/day.

The application of column

chromatog-raphy to the analyses of urines of different

age groups has made it possible to

deter-mine which amino acids are excreted in

greater quantities during the newborn

period. Of the 1 gm of free amino acids

cx-cmeted daily by the adult, 70% is composed

of taurine, glycine, histidine, and

methyl-histidine. Acid hydrolysis of urine of

adults demonstrates that about 2 gm more

122 AMINO ACIDS

Glycine, glutamic and aspamtic acids make

up the major portion of the conjugated

amino acids; in addition there are

signifi-cant quantities of conjugated proline,

cystine, semine, threonine, valine and

tyro-sine.

The excretion of amino acids of the

new-born infant differs from that of the adult

not only in quantity but also in pattern.

Those amino acids which comprise 70% of the

excretion of the adu’t comprise 45 to 55% of

the total in the newborn infant and about

35% of the total in the premature infant.4’

The following amino acids are excreted in

increased quantities in early life : threonine,

semine, glycine, alanine, cystine, leucine,

ty-mosine, phenylalanmne and lysine. Proline

and hydroxyproline are found in the urine

during early infancy but their presence has

not been reported in urine of adults. An

unidentified peak present in urine of infants

but not in that of the adult has a1so been

noted. The excretion of taurine is unique in

that it is present very early in life, then is

excreted in only trace quantities and then

reappears later as the pattern of excretion

of amino acids assumes that of the adult.

It is of interest to speculate on the cause

of this aminoaciduria of early life. Some

of it is due to immature renal, especially

renal tubular, function. However, the

Se-lective nature of this aminoaciduria

sug-gests that it may be a reflection of some

alteration in metabolism of protein during

early life.

In general, theme seems to be surprisingly

little correlation between diet and the

quan-tity and pattern of amino acid excretion. A

thirteenfold increase in intake of protein

resulted in only a two- to threefold increase

in excretion of a few of the amino acids.46

The one exception to this is the excretion

of 1-methyihistidine; the excretion of this

compound roughly parallels the quantity of

protein in the diet. In our work, complete

withdrawal of a single amino acid from a

synthetic diet, the protein of which is

com-posed entirely of amino acids, results in a

TABLE II

SUMMARY OF I)ATA ON COLUMN CHROMATOGRAPHY OF AMINO ACIDS IN NORMAL URINE AT DIFFERENT AGES4

(Expressed in mg per 100 gm total nitrogen)

Early Post- Full-term Older One- Year- Older Adults

Premature premalu,e Neonatal Period Infants Olds Cliildrn

Fowle,

tt aL”

Dusfin Fowle,

e1 at.” et at.

Duslin Fowler

etat. eta!.

Fowler el at.

. Fowler Stein and

al. ifooree

Duslin

,.j at.

Diet Evap.

Milk

Breast Evap. Milk Milk

Breast Evap. Milk Milk

Evap. Milk

Mixed Diet

Mixed Mixed Diet Diet

Mixed Diet

Taurine I .53 <7 Q77 68 tr 114 116 35

Threonine 550 80 67 48 49 23 5 3

Serine (asparagine,

glutamine) 333 631 135 WO 139 119 79 66 74 166

Glutamic acid 17 94 33 120 19 47 14 12 <8 <8

Glycine 1095 1330 68 974 56 337 approx 186 161 3.5t

Alanine 9O 9O 190 277 93 1 175 43 48 55

Cystine 71 61 34 130 41 33 14 <11 <8 <8

Valine ? 43 ? 35 ? P 11 8 <8 <8

Isoleucine 19 47 H 47 10 9 15 13 iS 9

Leucine 24 35 41 50 17 6 !) 1 10 9

Tyrosine 184 167 98 33 54 Ft 41 10 18 31

Phenylalanine 31 54 35 19 46 14 10 10 15

3-methyihistidine 39 <5 10 19 39

Histidine 115 376 11 156 88 178 87 113 130 196

Lysine

(1-methyl-histidine) 32 142 104 201 69 48 10 18.5 Ill 83

Methionine 17 <U 5 3 13 ?

Proline 810 178 ? 62 147 46 9 0 <8 17

Ilydroxyproline + + + 0 0

REVIEW ARTICLE

decrease in excretion of that particular

amino acid; stepwise reintroduction of the

amino acid to the diet is accompanied by a

gradual increase in its excretion.

Table II is a summary of data obtained

by column chromatography in various age

groups.

PECULIARITIES OF AMINO ACID

METABOLISM

DURING

PREGNANCY

AND IN THE FETUS

It has been known since 1923 that there

is some difference in the way amino acids

are handled during pregnancy.49 A

pemsis-tent increase in rate of the urinary

excre-tion of histidine during pregnancy was

re-ported. This finding has since been

con-firmed by several groups of workers.

His-tidinuria first appears at the time of

nida-tion of the egg, persists all during

preg-nancy and disappears during the first week

post partum.’#{176} There is a similar increase

in excretion of histidine just prior to the

onset of the menstrual period and this

dis-appears at the end of the period.

Waliraff et al.,51 using microbiologic

tech-niques, found that theme was an increased

excretion of 7 of the 14 amino acids which

they were able to assay. These included

histidine, tyrosine, arginine, phenylalanine,

semine, threonine and tryptophan. This work

was extended by Martin et al.,52 who found

that the total excretion of alpha amino

ni-trogen was increased during pregnancy but

that this was not accompanied by increased

concentrations of amino nitrogen in the

plasma. Specific study of the histidinumia of

pregnancy’3 demonstrated three important

causative factors : an increased glomerular

filtration rate, decreased tubular

reabsorp-lion, and an altered metabolism of histidine.

There is a much higher concentration of

amino acids in cord blood than in maternal

blood. The ratio of fetal to maternal

con-centration of alpha amino nitrogen in

plasma is between 1.6 and 1.8. Dent has

suggested that the placenta acts as a pump

of amino acids to the fetus. Theme is also a

greater concentration of amino acids in the

skeletal muscles of guinea pig fetuses than

in the maternal muscle and in both the

skeletal and cardiac muscles of the rabbit

fetus.

AMINO ACID IMBALANCES,

ANTAGONISMS AND TOXICITIES

Amino acid imbalance may manifest

it-self in three different ways. One, when the

diet is deficient in amino acids, an increase

in one may provoke a deficiency of the next

most limiting amino acid. Two, one amino

acid may actually be antagonistic to

an-other; thus an increased intake of th ‘first

amino acid must be accompanied by a

pro-portional increase in the second if normal

growth is to procede. Three, there may be

a specific toxic effect.

An example of the first type of imbalance

is the relationship that exists between

thre-onine and tryptophan in the 55 When

rats are fed a diet containing 9% casein, the

intake of threonine, cystine, methionine and

tryptophan is below the requirement and

the growth mate is 10 gm/week instead of

32 gm/week. When cystine is added in

amounts approaching the requirement,

growth is increased slightly to 12 gm/week.

If 0.04% threonine is then added, the growth

mate is depressed to 4 gm/week. The further

addition of tryptophan is necessary to

bring the mate of growth back to normal. If

the intake of threonine is increased without

giving a supplement of cystine, inhibition

of growth is not nearly so great as when

both are added.

Another example of imbalance,56

involv-ing lysine, is of special interest in view of

the recent publicity it has received as a

supplement in infant feeding. Weanling rats

were fed a diet which contained white flour

as the protein; this was supplemented with

lysine which is known to be deficient in this

protein. Maximum gain in weight and

con-sumption of food were obtained when 0.2

to 0.3% of L-lysine was provided. When 0.6%

of L-lysine was fed, there was a small but

124 AMINO ACIDS

and consumption of food. This became

more marked as the lysine supplement was

increased beyond this figure. Similarly,57 a

depression of growth was produced by

feeding L-lysine to dogs receiving a diet

low in content of protein. This depression

was only reversed when methionine was fed

simultaneously with the lysine.

Amino acid imbalance may cause

metab-olic disturbances other than the retardation

of growth. When 0.2% cystine or methionine

is added to the 9% casein diet, theme is a

marked accumulation of fat in the liver.’8

This can be prevented by the simultaneous

addition of the proper amounts of

threo-nine. When the intake of threonine is less

than the requirement, the addition of very

small amounts of methionine will result in

a high content of fat in the liver.

A true antagonism exists between leucine

and isoleucine.” The 9% casein diet

con-tains adequate amounts of both of these

amino acids. However, the addition of 3%

of leu#{243}ine causes a marked depression in

growth. Supplementation with isoleucine

completely counteracts the depressive effect

of 1.5% leucine. But that caused by the 3%

leucine is only partially counteracted by the

addition of isoleucine. Valine as well as

isoleucine must be added to the diet to

completely counteract this amount of

leu-cine. Part of this antagonism can be

cx-plained by the fact that leucine reduces

the intestinal absorption of isoleucine6o and

also apparently interferes with the renal

tubular reabsortion of isoleucine, since an

infusion of leucine greatly increases the

renal excretion of isoleucine.61 True

antago-nism has also been demonstrated between

phenylalanine, tyrosine and threonine.62

The toxicity of 12 amino acids was

re-cently determined by intraperitoneal

injec-tion in adult rats.63 Isoleucine was found to

be the most toxic and tryptophan the least.

Arginine was found to markedly reduce the

toxicity of a mixture of amino acids.

Gly-cine#{176}4is known to have a toxic effect that

can be counteracted by high levels of folic

acid. Moderate amounts of methionine65

cause a depression in growth when fed with

an adequate 18% casein diet unless vitamin

B6 is also provided. However, even large

amounts of vitamin B6 are incapable of

pme-venting the growth depression produced by

large amounts of methionine.

AMINO ACID REQUIREMENTS

Each amino acid must be available in the

proper amount to be efficiently utilized in

the synthesis of tissue protein. Amino acids

which cannot be synthesized at all or in

proper quantities have been termed

essen-tial by Rose66 and these must be supplied

by the diet. The unessential amino acids

spare the essential ones by providing

ni-trogen for synthesis. Diammonium citrate

and ammonium acetate and urea also can

provide extra nitrogen.676’ The time of

ab-sorption of each amino acid in relation to

the others is also important.

demonstrated that delayed supp1ementation

of diets with either tryptophan, lysine, or

methionine resulted in poor growth of mats.

Rats do not grow if five of their essential

amino acids are fed one hour and the

re-maining five are fed the next hour.72

Requirements of amino acids are

influ-enced by the adequacy of the other

constit-uents of the diet. Caloric intake must be

adequate or some phases of amino acid

metabolism may be directed to provide

calories. The adequacy of the intake of

vita-mins is also of importance; pyridoxine is

intimately concerned in amino acid

metabo-lism. If theme is a deficiency of

nicotina-mide, some tryptophan will be diverted

along this metabolic pathway and the

tryp-tophan requirement will then be increased.

The presence or absence of certain

unessen-tial amino acids influences the requirement

of the essential ones; the requirement of

phenylalanine can be substantially reduced

by the presence of tyrosine, and require-ment of methionine is reduced when cystine is also present.

Theme are four different techniques that

may be used in the study of requirements

pro-.-. TOTAL S(PUM PROT(a pj

*-o SCRUM ALSUMIW

I-. stRuM cLoeuLIN

(GRAM P(R 00 cc) NITROGEN

RETENTION

MG/aC/DAY

WIGNT

IN

RI LOGRAM S 2O

+100

r

3.5

INREONINC 1P474115

______

MG/KG/DAY

teins may be fed and then supplemented at

different levels with the deficient amino

acid. However, such foods may also be

de-ficient in other amino acids and occasionally

there actually can be an imbalance of amino

acids. 2) Proteins can be degraded to

de-stroy one amino acid and this amino acid

reintroduced at the desired leve1. With this

procedure, there is always the uncertainty

of knowing all that is done by the

degrada-tion process. 3) The dietary nitrogen may be

provided by mixtures of pure amino acids.

The one disadvantage to this method of

approach is that the caloric requirement is

higher when pure amino acids are fed than

when unhydrolysed protein is used. 4)

Limiting values for requirements of amino

acids may be calculated from food mixtures

on which theme has been good clinical

prog-mess. This method indicates that the

mini-mal requirement is not greater than the

in-take on which there is satisfactory progress,

but does not indicate the minimal

require-ment.

Although the amino acid requirements

of adults have been studied fairly

exten-sively, we know of no studies in children

except those made by our group at New

York University in infants. Most recently

these studies have been carried out on a

synthetic diet, the protein moiety of which

is composed of 18 synthetic L-amino acids.

After the synthetic diet was fed for a

pe-nod, the amino acid under study was

dropped out and then reintroduced in a

stepwise fashion until normal growth was

obtained. The content of nitrogen in the

diet was kept constant by the substitution

of glycine. Our criteria of normal growth

included the gain in weight, retention of

nitrogen, and concentrations of plasma

pro-tein. Exploratory studies were also made in

the excretory pattern of free amino acids in

the urine by both paper and ion exchange

column chromatography.

Approximately 60 mg of threonine per

kilogram per day is sufficient for infants 1

to 6 months of age. This amount allows

nor-mal gain in weight, good retention of

nitro-T..:

.4--L.

=-‘-.-r

-____

MM OtMSt

FIG. 1. Threonine requirement of the normal in-fant (Baby He, 2 weeks of age). Satisfactory gain

in weight and retention of nitrogen were obtained with an intake of 58 mg/kg but not on an intake

of 30 mg/kg.

gen, and maintains the concentrations of

plasma protein. Figure 1 is a graphic

repre-sentation of the protocol concerning one of

these subjects. There was also a decreased

urinary excretion of threonine during the periods of deficiency.

An intake of 90 mg/kg of phenylalanine

and an intake of 90 mg of lysine7’ per day

!!‘1

44:!

Ihu

:z-

rA*x ,..1___iN , p , , ma

-Irl_ #{149} .5 L1_iv

I ,i a a a a i a a a) a a

stag_I

---_

-FIG. 2. Requirement for phenylalanine of the

nor-ma! infant (Baby Sa, 6 months of age). Gain in

weight and retention of nitrogen were not

ade-quate when receiving 61 and 63 mg/kg but with

- . , i! . . .

NITROGEN 2

(Mc/KG/iflfl_iL__i_U

DIARRHEA-I #{149}#{149}

7.5

WEIGHT .o .. ..

II’.l :

:

KILOGRAMS #{149} . . , . ... .

a ... :

as : : : :

:275: :

LYSINE HCI INTAKE :.

(MG/KG/DAY) w1:aL$

:

-i

MARCH APRIL

: 3K 34 : fl

Fic. 3. Requirement of the normal infant for lysine (Baby Cl, 1J months of age). Sat-isfactory gain in weight and retention of nitrogen were obtained with an intake of

1 10 mg of lvsine HC1 (89 mg of lysine) per kilogram.

2#{243}2 i lb 6 30

JUNE

126 AMINO ACIDS

TOTAL. SCRUM 0

. PR9TEIN

4ERUM ALBUM,

3ULl t:’5RAM PER oCc)

were able to fulfill our criteria of adequacy. Figures 2 and 3 are sample protocols of these studies. The urinary excretion of these two amino acids also paralleled the intake.

Of note too, is the hypoglobulinemia that

accompanied the periods of phenyla1anine deficiency.

Thus far, only two studies of the require-ment of valine76 have been completed. An intake of 85 mg/kg was sufficient for one

infant (Fig. 4) and an intake of 105 mg/kg

was sufficient for the other 1-month-old child.

Histidine was originally classified as an

essential amino acid by Rose who found it to be necessary for growth in rats. In his studies on adult human males, however, he

h

I

found that nitrogen equilibrium could be

maintained without it and classified it as

unessential for the human adult.77 However, histidine has proven to be an essential

amino acid for the three infants we have

studied thus far.76 All three ceased gaining

weight when it was removed from the diet

and the retention of nitrogen gradually fell

off. An intake in the neighborhood of 35

mg/kg/day was sufficient to allow normal gain in weight and retention of nitrogen (Fig. 5).

Arginine76 does not seem to be essential

for the human infant. Three infants have

now been maintained for periods of 1

month each while ingesting a diet free of

nor-I

z!F:

KOGRAMS

VALINE INTAKE

(MG/KG/D

3o :

:1

I#{149}7

$50 I I

‘:w:PiAAI 0

L!J

$3.3 ;

I 5 10 15 :ao 10 to t o

APRIL MAY

Fic. 4. Requirement of the normal infant for valine (Baby Mi, 1 month of age).

Gain in weight and retention of nitrogen were satisfactory with an intake of 83

and 85 mg of valine per kilogram.

127

TOTAL SERUM I0

. PRQTEIN

SERUM ALBUMN

. 0 S

SERUM GLOBULIN

K K K

(GRAM PER 100 CO

mal rate and retention of nitrogen was

cx-cellent during the entire period of time. No

other clinical or chemical abnormalities

were noted.

Our data have been confirmed by the use

of a natural diet.78 This consisted in

gmadu-ally reducing the content of milk in a

form-ula of evaporated milk while keeping the

ca-loric intake constant by the addition of

sup-plements of carbohydrate and fat. The

lowest intake of milk which allowed good

gain in weight, when supplemented with

glycine to provide nitrogen from an

unessen-tial amino acid, supplied amounts of

threonine, phenylalanine, lysine, valine and

histidine similar to those which were the

end points in our studies of minimal

re-quimements (Table III).

SYMPTOMS

OF SPECIFIC DEFICIENCY

OF AMINO ACIDS

From a knowledge of the metabolic

func-tion of the amino acids, it would appear

that the deficiency of a single amino acid

might give rise to two types of symptoms:

those which are related to the general

func-tion of protein synthesis and those related

to the specific function of the individual

amino acid. In the first group are the same

symptoms that are usually ascribed to

de-ficiency of protein : loss of weight, poor

growth, fatigue, lack of energy, irritability,

decreased resistance, retarded wound

heal-ing, hypoproteinemia, anemia and

nutri-tional edema.

There are a number of examples of

sin-128 AMINO ACIDS

WEIGHT

IN

KILOGRAMS

3OO

I

o1

I

‘331

,oo-I

!

#{149}

1

I

50 BEEF PPIOTEINI 122.4 33.6

1

0 HISTIDINE

0 , #{149} I I I I 1 I I 1 1 I I I

10 15 20 25 30 5 10 20 30 5 10 5 20 25 30

MARCH APRIL MAY

Fic. 5. Requirement of the normal infant for histidine (Baby Li, 53i months of age). The gain in weight ceased and retention of nitrogen was decreased when histidine was removed from the diet. An intake of 33.6 mg/kg permitted satisfactory gain in weight

and retention of nitrogen.

TOTAL SERUM

PROTEIN

SERUM ALBLfrAN

SERUM GLOBULiN

x- -x x

GRAM PER 100CC)

NITROGEN

RETENTION

(MGII<G/DAY)

HISTIDINE INTAKE

(MG/KG/cAY)

gle amino acid in experimental animals.

Dc-ficiencies of phenylalanine,7#{176} thmeonine,8#{176}

histidine,81 and tmyptophan82 result in

me-gression of the size of the anterior pituitary

acidophils, depletion of the anterior

pitui-tary gonadotrophic basophuls, atrophy of

the testis, and thymic involution; none of

these changes were present in pair-fed

semi-starved control mats. In addition, deficiency

of tryptophan is also accompanied by

for-mation of cataracts,83 lipoidosis of hepatic

cells, myocardial lesions and crystalline

de-posits in the involuted thymus. In most

studies of experimental deficiency in man,

specific symptoms have not been described;

this may be due to the short duration of

such studies. However, a striking

diminu-tion in the spermatozoa count was noted on

the ninth day of arginine deprivation in the

study of Holt and Albanese;84 this was

re-versed by supplementation of the same diet

with arginine. Thus far, no clear-cut

cvi-dence of specific deficiencies of amino acids

have been described as occurring

sponta-neously in man.

KWASHIORKOR

Kwashiomkor is the term that has been

applied to a protein deficiency disease which

129

TABLE III

REQUIREMENTS OF INFANTS FOR ESSENTIAL

AMINO Acws

Amino Acid

Studies on Mixture of

18 L-amino ACid.R

(mg/kg/day)

(‘alcidoied

from

Inlakes on Minimal

Milk Diet (mg/kg/day)

Arginine 0 42

Histidine 35 24

Isoleucine 75

Leucine 135

Lysine 90 83

Methionine 32

Phenylalanine 90 61

Threonine 60 51

Tryptophan 16

Valine 85 80

America. The name arose among the Ga

tribe of Accra, the capital of the Gold Coast,

and describes the child as “deposed.”8’ This

refers to the fact that this disease usually

occurs at the time breast feeding is stopped

because of the birth of a new sibling. Thus,

the highest age of incidence is between 1

and 3 years. In Latin America, this

syn-drome is known as “SIndrome Pluricarencial

de la Infancia.”

Clinically, theme is retarded growth,

apathy and peevishness, edema,

dyspigmen-tation and dermatoses. Dyspigmentation

re-fems to the hair which may either be

bleached or changed to a reddish color. The

texture of the hair is also altered; it may be

coarse, dry, sparse, and easily pulled out.

A variety of skin disorders have been

de-scribed including dyspigmentation,

hyper-pigmentation, “enamel paint dermatoses,”

crackled skin, linear fissures, dryness and

desquamation. Gastrointestinal disorders

are inconstant and irregular and may

in-dude anorexia, vomiting and diarrhea. The

liver is often enlarged, and biopsy of the

liver invariably shows fatty infiltration,

either occurring by itself or in combination

with necrosis and fibrosis. One of the most

consistent biochemical findings is a

depres-sion in the concentration of albumin in the

serum. Since this is often associated with an

increased concentration of globulin, the

con-centration of total protein may not be

ab-normal. The increase in concentration of

globulin occurs in the alpha as well as the

gamma fraction. The production of

du-odenal and pancreatic enzymes is reduced,

and absorption of fat is interfered with.

Although the mortality rate is very high in untreated patients and in those who come

to medical attention late, it has been known

for some time that kwashiorkor can be

cured by feeding milk. Brock and Hansen86

have been able to prove that this is

pri-manly a protein deficiency disease; they

had similar rates of cure in groups treated

with mixtures of skim milk with and

with-out supplements of vitamins and with

ca-scm with and without supplements of

vita-mins. They have been able to extend this

work to demonstrate that the curative

fac-tom is the amino acid composition of the

ca-scm and not any unidentified factors that it

may contain. The use of a synthetic diet,

containing a mixture of amino acids as the

sole source of protein resulted in an equally

good rate of cure.

It is possible that deficiencies of specffic

amino acids may play a part in the etiology

of this disease. Some preliminary

observa-tions on patterns of urinary excretion of

amino acids have been carried out by our

group at New York University using column

chromatogmaphy.8 The abnormal findings

included an increased excretion of

isoleu-cine, a much higher excretion of

phenylal-anine than tyrosine (normally more

tyro-sine is excreted than phenylalanine) and a

diminished excretion of threo#{241}ine. At

pres-ent it is difficult to interpret these findings. However, the increased excretion of

phenyl-alanine suggests a failure of its normal

con-version to tyrosine which may be a result

of impaired liver function. This may explain

the clinical picture of dyspigmentation.

THE AMINOACIDURIAS

Dent88 has divided the aminoacidurias

into 1) those caused by overflow, and 2)

those due to renal mechanisms. In the first

130 AMINO ACIDS

amino acids is increased simultaneously

with, and presumably as a result of,

in-creased concentrations in the blood. In the

second category, theme is increased

excre-tion of amino acids while the concentrations

in the blood

remain

normal.

Each

of these

two types of aminoacidumias may be further

subdivided into the inborn and acquired forms.

OVERFLOW AMINOACIDURIAS

Thus far, few of the aminoacidumias have

been corre!ated with increased

concentra-tions in the blood. Among the acquired

forms are the aminoaciduria which occurs as

a result of the rapid infusion of a protein

hydmolysate, and that which occurs as the

result of certain types of liver disease. The

only proven inborn aminoaciduria related

to abnormal concentrations in plasma is

phenylketonuria.

Liver Disease

There have been numerous reports of

dis-turbances in metabolism of amino acids in

liver disease. This may occur in relatively

mild derangements of the liver such as

in-fectious hepatitis in childhood as well as in

the more severe forms of disease. Hsia and

Gellis89 were able to study excretion of

amino acids in 18 children with infectious

hepatitis. Of these, six had moderate

amino-aciduria as .shown by urinary excretion of

amino nitrogen which averaged 3.7 mg/kg/

day (their normal is 1.9 mg/kg/day) and six

had a borderline aminoacidumia of 2.4 mg/

kg/day. Those children who had severe

aminoacidumia all had concentrations of

amino nitrogen in the plasma greater than

5 mg/100 ml; 5 mg/100 ml was the greatest

value found in any of the controls. Paper

chromatography revealed increases in the

amounts of the amino acids usually seen in

the urine with this technique (alanine,

glu-tamine, glycine and serine) as well as

iso-leucine, leucine, lysine and methionine.

The aminoacidumia disappeared promptly

with recovery except for the persistent

in-creased excretion of glutamine.

Three patterns of abnormal amino acid

excretion in infectious hepatitis in adults

have been described by Dent and

91 These include a moderate

in-crease in the excretion of many amino acids,

an increased excretion of cystine alone, and

an increased excretion of cystine along with

beta-aminobutyric acid. Chronic disease of

the liver and infiltrations into the liver have

been associated with the excretion of

cys-tine alone or cystine in combination with

beta-aminobutyric acid, methylhistidine,

and taurine. The excretion of large amounts

of all the amino acids occurs with acute

yellow atrophy. This is probably due to autolytic processes in the liver which cause

the breakdown of protein, releasing large

amounts of amino acids into the blood

stream which are subsequently excreted.

The milder aminoaciduria of the less severe

forms of liver failure may be due to faulty

deaminization by the liver.

An investigation92 by paper

chromatog-raphy of the concentrations of eight amino

acids in the plasma in patients with liver

coma has revealed consistent increases of

the following amino acids : glutamic acid,

glutamine, tymosine, cystine and methionine.

Phenylketonuria

Phenylketonuria is an hereditary disorder

in which an aminoacidumia is correlated

with an increased concentration of an amino

acid in the blood. Theme is an absence of

the liver enzyme which is normally

respon-sible for the conversion of phenyla1anine to

tymosine.9’ As a result, theme is an

accumula-tion of large amounts of phenylalanine in

the blood and cerebmospinal fluid’4 and the

excess phenylalanine is excreted in the urine

both in the unchanged form and in the form

of abnormal metabolites.#{176} The

concentra-tion of phenylalanine in the serum may be

as great as 60 mg/100 ml while the

cerebro-spinal fluid may have as much as 8 mg/100

ml. Abnormal metabolic end products which

are excreted in the urine consist of

phen-ylpyruvic acid, phenyllactic acid and

amounts of other metabolites such as

0-hy-droxyphenylacetic acid and other indole

products derived from tymosine and

trypto-phan.’6

Clinically, the typical child with

phenyl-ketonuria is fair-haired and -skinned with

blue eyes; his skin is quite susceptible to

dermatitis. Theme are, however, red- and

brown-haired exceptions to this. The

ma-jomity of the children are seriously retarded mentally, although a few cases of

border-line intelligence have been reported. About

25% have some sort of epileptic seizures and

the percentage with abnormal

electroen-cephalogmams may be even higher. Various

neumologic abnormalities may also be

pres-ent.

There has been renewed interest in this

disease recently because of its treatment

with a diet poor in content of

phenylala-nine. It is logical to infer that if the mental

defect is caused by the presence of

abnor-mal metabolites, then their removal might

result in improvement. A number of

chil-dren have been treated by this diet.#{176}799

The biochemical features of the disease

have been entirely reversed: the

concentra-tions of phenylalanine in the blood became

normal and the abnormal metabolites

dis-appeared from the urine. There has been a

rather general alleviation of the convulsive

disorder with concomitant improvement in

the electroencephalogram. Theme has also

been a widespread improvement in the

be-havior disorders. There has not been a

uni-form success in the improvement of the

in-telligence. This difference in therapeutic

success is probably related to the age at

which treatment has been instituted: the

younger the child, the more chance for

suc-cessful treatment. No one has reported

in-tellectual improvement when treatment has

been instituted after the age of 2 years.

Horner and Streamer10#{176} have recently

me-ported a case in which treatment was begun

at 8 weeks of age; this child at 9 months of

age has continued “to develop at the upper

normal levels in all areas for his age.”

Because of the possibility of successful

treatment, theme is an urgency to the early diagnosis of this disease. It would seem that

the usual screening test for the discovery of

phenylketonumia, the addition of a few

drops of 5% fermic chloride to acidffied urine

with the development of a blue green color,

cannot be used in the newborn period. Arm-strong and Binckley,101 who studied a

pa-tient from the time of birth, found that

phenylpymuvic acid did not appear in the

urine until the infant was about 1 month

old and then, not in quantities that could be

detected by the simple qualitative test.

However, concentrations of phenylalanine

in the plasma were abnormally great as

early as the fifth day of life.

RENAL

AMINOACIDURIAS

The renal aminoacidurias may also be

divided into the inborn and acquired forms.

Among the inborn forms are cystine storage

disease with aminoaciduria and dwarfism,

cystinumia, galactosemia, Wilson’s disease,

and a few other syndromes associated with

mental deficiency that have not as yet been

well classified. Among the acquired forms

of renal aminoaciduria are scurvy, rickets,

and poisonings.

Cystine Storage Disease with

Aminoaciduria and Dwarfism

Probably the most massive aminoaciduria

yet observed occurs in this syndrome. This

is the disease that Lignac102 described in

1926, and the one that Fanconi,103 de

Toni,104 and Debr#{233}’#{176}’have all studied and

as a result has come to be known by various

combinations of their names. There is a

great variation in the clinical picture and

also in the age of onset. The clinical

mani-festations are reflections of the metabolic

disturbances and include dwarfing and

wasting, rickets and osteoporosis, pymexia,

eye changes, anorexia and vomiting,

poly-dipsia and polyuria, dehydration, acidosis,

profound collapse and sudden death.

Among the metabolic abnormalities of the

albumi-132 AMINO ACIDS

nuria, hypophosphatemia and

hypopotas-semia. The acidosis is the result of several

disturbances which include abnormal loss

of bicarbonate, poor formation of ammonia

in the kidney and an increased excretion of

fixed base. There is also an increased

cx-cmetion of organic acids associated with an

increased concentration in the plasma. The

glycosuria is renal in origin since it is

ac-companied by a normal concentration of

sugar in the blood. Although theme is great

variability in the biochemical abnormalities

just described, two metabolic disturbances

are consistently found. These include

cys-tine storage and gross aminoacidumia.

Ab-normal deposits of cystine are found most

frequently in the bone marrow, cornea, and

conjunctiva. Bickel et al.b06 found evidences

of cystine storage in all 14 of their cases and

a massive aminoaciduria in all 13 of the

cases in which they looked for it.

The aminoacidumia may be so excessive

that it may comprise as much as 13% of the

total excretion of nitrogen. Between 10 to

20 amino acids have been demonstrated to

be present in excessive quantities in the

urine. These include the leucines, valine,

ly-sine, proline, cystine, aspartic acid, tyrosine, phenylalanine and threonine. The urine pattern resembles that of normal plasma.

The type and quantity of aminoacidumia

varies from one case to another and from

day to day in the same case.

Dc Toni107 believes that the disease he

originally described is not the same as that

first described by Lignac and should not be

classified with it as a single entity. He

pre-fers the title “renal rickets with

phospho-gluco-amino-renal diabetes,” a name that

includes all the salient features of the

syn-drome. He has several reasons for

separat-ing this syndrome from cystinosis. Renal

diabetes and dwarfism are always present

in the de Toni syndrome and are inconstant

findings in cystinosis. The prognosis is

bet-ter in the de Toni syndrome than in cystine

storage disease; patients with the former

disease do reach adulthood. Both lead

poi-soning and vitamin D intoxication may be

etiologic factors in some cases of the de

Toni syndrome; they do not have any role

in cystinosis. Cystine storage may or may

not be present in the de Toni syndrome but

always occurs in cystinosis. He does think

that both conditions can coexist in the same

individual, the phospho-gluco-amino-menal

diabetes occurring as a complication of the

cystine storage disease.

The question as to whether the

amino-aciduria is renal in origin or represents

overflow from increased concentrations in

the blood is an important one in trying to

elucidate the pathogenesis of the disease.

There is, however, a divergence of opinion.

Dent classified it as a renal aminoaciduria.

Harper et al.b08 studied the concentration

of total amino nitrogen of the plasma and

the concentrations of seven individual

amino acids and found them all to be within

normal limits. The content of amino acids

in the plasma of four of the patients studied

by Bickel was determined microbiologically

by Schmeiem and some abnormalities were

noted. These included a 100% increase in

content of tryptophan tymosine, phenyl

alanine, leucine, isoleucine, cystine and

methionine and a 50% increase in threonine,

valine, lysine and amginine. For this reason,

Bickel believes that this disease is primarily

an

that other abnormalities are secondary to

this. The other view is that there is an

in-born functional defect of the resorptive

capacities of the proximal tubules which is

responsible for the aminoacidumia, the

gly-cosumia, and the increased loss of base. This

is the opinion of Dent,109 Fanconi,11#{176} and

McCune.111 Morphologic anomalies of the

renal tubules have been demonstrated by

Clay et al.h12 who used micmodissection

methods. These changes, which have not

been previously described in any other type

of kidney disease, include a first

convo-luted tubule which is shorter than normal

and is joined to the glomerulus by a narrow

swan-like neck. The distal tubule is thin and

there is atrophy of the epithelium. Clearly,

these two opposing theories can be

dis-carded. It is, of course, quite possible that

both of these abnormalities may coexist in

the syndrome.

Cystinuria

Cystinuria is a much more common

con-dition than cystine storage disease with

aminoaciduria and has a much more benign

course. These patients excrete large

quanti-ties of cystine, lysine, ornithine and

occa-sionally arginine.113 This is presumably due

to a failure of the kidney to reabsorb these

amino acids. The blood level of cystine is

within normal limits and no abnormalities

of the metabolism of sulfur-containing

amino acids could be demonstrated when

they were fed in excess.1” There is no

de-position of cystine in the tissues. The only

untoward effect is the formation of cystine

stones in the genitourinary tract and the

secondary renal damage which may ensue.

Galactosemia

The gross 116 which

oc-curs in galactosemia is most probably due

to diminished renal tubular resorption

which results from renal irritation by the

excreted galactose. When galactose is

re-moved from the diet,”7 it takes several days

for the aminoaciduria to disappear and,

con-versely, it takes several days for the

amino-acidumia to reappear after galactose is

me-introduced into the diet. Aminoaciduria did

not appear until 3 months of age118 in one

infant who was studied from the time of

birth although galactosemia was a constant

finding. Amino acids in plasma are also

normal.h19 The aminoaciduria of

galacto-semia consists mainly of the following

amino acids : serine, glycine, threonine,

alanine, valine, the leucines, tyrosine and

glutamine.

Hepatolenticular Degeneration (Wilson’s Disease)

?fhi degenerative disease of the basal

ganglia associated with a disorder of the

liver and Kayser-Fleischer ring has recently

been shown to be accompanied by a

mas-sive aminoaciduria.12#{176} Threonine and

cys-tine are excreted in the greatest excess but

there is also a large increase in proilne,

citrulline, serine, glycine, asparagine, valine,

tymosine and lysine. There is a small

in-crease in histidine, omnithine and

phenyl-alanine output and theme is also reduced

excretion of taurine and 1- and

3-methyl-histidine. It has been postulated that the

abnormal accumulation of copper which

occurs in the lenticular nucleus and in the

liver and accounts for the ciinical picture

also takes place in the kidney and causes

tubular damage and is hence responsible

for the aminoaciduria. There is an increased

urinary excretion of copper in Wilson’s

dis-ease which parallels the amount of amino

acids excreted.121 However, there is nothing

to suggest that the amino acids are

cx-creted together with the copper as a

corn-plex.

The amino acids in the plasma are within

normal limits until late in the disease when

theme is much liver damage. However,

ceru-loplasmin, the major copper-containing

pro-tein of the serum, is reduced; this is the

most specific biochemical abnormality of

the disease.”2 Other information which

sug-gests that the aminoaciduria is renal in

origin arises from feeding large meals of

protein. When a normal control ingests a

meal rich in protein theme is relatively little

increase in the urinary excretion of amino

acids; when a patient with Wilson’s disease

takes the same meal there is a great

in-crease in the aminoaciduria in spite of the

fact that the concentration of amino acids

in the plasma remains normal. However, a

simple failure of tubular reabsorption does

not completely explain the aminoaciduria

since this does not account for the amino

acids which are excreted in less than

nor-mal quantities.

One other interesting facet to the

amino-aciduria of hepatolenticular degeneration is

a report that it occurs in asymptomatic

134 AMINO ACIDS

Other Aminoacidurias Associated with

Mental Deficiency

Lowe et al.124 described a peculiar

syn-drome in which aminoaciduria was one of

several chemical abnormalities. Clinically

these three infants all had severe mental

re-tardation, hyporeflexia, flabby musculature,

hydrophthalmos and intermittent fever

with-out obvious cause. Two had cataracts.

Without specific therapy two of these

pa-tients had either rickets or osteomalacia.

There was systemic acidosis as manifested

by a low content of carbon dioxide in the

blood and low pH. There was a decreased

ability of the kidney to produce ammonia

and an increased excretion of organic acids.

Aminoaciduria was responsible for some of

the organic aciduria. As much as 7% of the

urinary nitrogen was excreted in the form

of amino nitrogen. Paper chromatography

revealed this to be due to generalized

ami-noaciduria. A case of an “obscure

syn-dmome described by Bickel and

Thursby-Pelhamhl8 is also probably the same disease,

the only seeming difference is that their

case did not exhibit any increase in

excme-tion of organic acids other than amino

acids.

Thelander and Imagawals5 have recently

reported six cases of aminoaciduria

asso-ciated with mental deficiency and various

congenital abnormalities most of which

in-volved the eyes. There has not been any

investigation as to which amino acids are involved.

A new familial syndrome in which

amino-aciduria is a cardinal symptom has

tenta-tively been designated as the Hartnup

syn-dmome.126 The clinical picture is inconstant

but includes a mild photosensitivity of the

skin which sometimes flares up to a

genem-alized rash of the exposed surfaces identical

with classic pel1agra, a severe cerebellar

ataxia which occurs when the rash is severe

or when there is a febrile episode but is

ab-sent at other times. Mental retardation has

thus far occurred only in the elder siblings.

The gross aminoaciduria differs from other

types of aminoaciduria in that theme is no

abnormality of excretion of proline. There

is also a striking indicanuria with excess

cx-cretion of indican and indolacetic acid.

A Familial Tubular Defect in Absorption of Glucose and Amino Acids

A single report of a tubular defect in the

absorption of amino acids and glucose was

made by Ludem and Sheldon.127 This

syn-drome is familial and occurred in three

gen-emations. The patients were asymptomatic,

except that one was of small stature.

Glu-cose tolerance curves were normal. The

aminoacidumia was massive and generalized.

Scurvy

J

an aminoaciduria in scurvy. There was a

large increase in the total amino nitrogen

excreted in two cases; this was a reflection

of an increase in excretion of some of the

amino acids. Column chromatography

me-vealed pronounced increases in the

excre-tion of taurine, threonine, semine, glycine,

alanine, histidine and lysine. There was a

moderate increase in excretion of tymosine

and a slight increase in excretion of

phenyl-alanine. The concentrations of amino acid

in the plasma were all normal;’7 hence this

is probably another aminoaciduria related

to reduced tubular reabsorption of amino

acids.

The defect in metabolism of

phenylala-nine and tymosine in premature infants

de-scribed by Levine, Mamples, and Gordon12m1

results in the abnormal excretion of

p-hy-droxyphenylpyruvic and

1-hydroxyphenyl-lactic acids. This spontaneous defect seen in

infants fed diets rich in protein was noted

as early as the fourth day of life and per-sisted as long as vitamin C was withheld. It was abolished in every instance by the

ad-ministration of vitamin C. Full-term infants

did not demonstrate this spontaneous defect

but it was precipitated in one infant by

feeding 1 gm of phenylalanine and in

an-other, by feeding 1 gm of tyrosine. Norton

et al.,130 using paper chromatography, found