FREE AMINO ACIDS IN NERVOUS TISSUE 475 
Betaines. It is claimed that the Coenzyme A esters of y-butyrobetaine, crotonbetaine 
and carnitine occur in mammalian brain, and that the free betaines accumulate in brain 
after chemically induced convulsions or electroshock*: 8°, These observations have 
as yet not been verified. 
Glycine betaine?’ #9 and homarine (N-methylpicolinic acid)47,49.%* occur in the 
axoplasm of squid giant nerve. The concentrations found are, for betaine, 73.65 
(Loligo pealti) and 119.11 (Dosidicus gigas) wmoles/g fresh axoplasm; for homarine, 
20.36 (Loligo) and 21.40 (Dosidicus ) umoles/g (ref. 46). 
y-Guamdinobutyric acid (Table IA). This substance has been isolated from calf 
brain and identified unequivocally*’. It occurs in brain in very small quantities*®. 
McLennan!!¢ has presented evidence indicating that y-guanidinobutyric acid occurs 
in Factor I (see under y-aminobutyric acid) and accounts for some of the properties 
of the extract. 
Aspartic acid and asparagine (Tables [A and B). Kress®® has reported that unless 
tissues to be analyzed are either frozen at once or extracted with two volumes of 
acid at least as strong as 0.5 N HCl, amounts of aspartic acid and asparagine 10-100 
times the control values are found. Since values in the literature for the brain aspartic 
acid of different species of vertebrates are at least 50 times that reported by KREgs*? 
for sheep brain, it is apparent that the question of “true” aspartic acid levels bears 
reinvestigation. Nevertheless, the figures for aspartic acid given in Tables IA and B 
are sufficiently consistent to warrant their inclusion as “normal” figures; however, 
most results obtained with vertebrate tissues not extracted with acid have been 
excluded from the table as being probably too high’: }, 39, 57, 127, 136, 154. The figures 
for the hen!86 have been retained as illustrative of the variation between brain, 
spinal cord and nerve. The extremely high concentration of aspartic acid in inverte- 
brate nerve*® %, 109 has already been noted. 
The distribution of aspartic acid in parts of the human brain has been studied 
by Oxumura e¢ al.!27, Studies on the variation with age indicate that there is 
less aspartic acid in immature brain than in adult brain™, 22, 127, 148, 
N-Acetylaspartic acid (Table IA). A major part of the non-protein aspartic acid in 
brain is present as the N-acetyl derivative. This compound is of particular interest 
in that it occurs only in nervous tissue!®!, but whether it performs any special role 
related to the functioning of the brain is not yet known. In the newborn rat and 
rabbit, the acetylaspartic acid concentration in the brain is Jow (approx. 1.1 wmoles/g) 
and there is a rapid increase to adult levels by approx. 20 days of age®*, 1°. An 
increase with age occurs in human brain also§®, 127, The concentration of the com- 
pound is highest in cerebral gray matter)®. 
Glycine and alanine (Tables IIA and B). These amino acids are present in moderate 
amounts in vertebrate brain and nerves, and in large amounts in certain invertebrate 
nerves. The possible presence of a glycine-containing lipid in rat brain has been 
noted®. Fetal mouse brain contains more alanine than adult brain!®. 
Serine, phosphoserine and threonine (Tables IIA and B). By virtue of its hydroxyl 
References p. 482/485 
