FREE AMINO ACIDS IN ANIMAL TISSUE 295 
increase in content of this amino acid can probably be attributed to continued fost 
mortem activities of the glutamic acid decarboxylase, the enzyme which forms 
GABA and which can function anaerobically, and the cessation of the tricarboxylic 
acid cycle which must furnish a-ketoglutarate, one of the substrates of the y-amino: 
butyrate transaminase system, probably the major system by which GABA is utilized 
in brain. Glutamine decreased in content between 8 and 12h and was no longer 
detectable after 24 h. It was probably decomposed into glutamic acid and ammonia 
by the action of cerebral glutaminase. The increases noted in the aspartic acid content 
could be attributable to formation by transamination from oxalacetate or by break- 
down of N-acetylaspartic acid, which is present in large amounts in brain?*. The 
increase in alanine could possibly result from transamination of pyruvate with a 
number of the available amino acids. Proteolytic activity probably accounts for the 
relatively small increases which were observed in the contents of threonine, lysine, 
valine, leucine and isoleucine, tyrosine and histidine. Ethanolamine phosphate was 
destroyed slowly, probably by action of phosphomonoesterases present 1n brain. 
One of the chief points of interest in the study with the Walker carcinoma was to 
ascertain whether the liberation of free glutamine, which has been found to occur 
during the treatment of a variety of animal tumors with agents which produce 
regression®*, would also take place under conditions of sterile autolysis. The results 
(Figs. 39-46) showed that only a small amount of glutamine appeared during the 
first 24h of autolysis in the samples of tumors studied, while valine, the leucines, 
tyrosine and some of the other amino acids were liberated from the tissue proteins 
at a rapid rate. At later time intervals more glutamine appeared. The changes, 
which occur after treatment with chemical agents*4 or during regression resulting 
from genetically determined resistance of the host?>, do not appear to be the same 
as those which occur when the tumor is allowed to autolyze under sterile conditions. 
In Figs. 47-58 are shown comparisons of the chromatograms obtained from freshly 
dissected samples of liver, kidney, muscle and brain with those obtained at 8 and 
24h after sterile autolysis. It is seen that in the case of liver extensive overall pro- 
teolysis had taken place rather rapidly, while the brain showed relatively little 
liberation of ninhydrin-reactive constituents. The kidney and muscle were inter- 
mediate in their rates of breakdown. An interesting finding in the case of the liver 
was that free arginine was not detected at any time but only ornithine, reflecting 
the great amount of arginase activity in the liver. In the kidney considerable orni- 
thine was formed but arginine was also detected, while in the case of muscle there 
was relatively little if any ornithine formed and the free arginine had considerably 
increased as a result of the autolytic process. The amounts of ornithine found 
are in keeping with the relative arginase activities in these tissues, which in mice 
were found to be for liver, kidney and muscle, respectively, 300, 6 and 1 (ref. 26). 
Another interesting finding is that in none of the tissues were there detectable 
changes in the level of taurine at any of the periods of autolysis which were observed. 
In liver, kidney, and muscle relatively rapid increases took place in the content of 
free valine, leucine and isoleucine, and tyrosine, whereas relatively small changes 
took place in some of the other detectable constituents. In particular, little increase 
if any took place in the content of glycine in the muscle during the period of obser- 
vation at a time during which considerable increases in the above free amino acids as 
well as lysine and arginine were observed. It is apparent from cursory examination 
References p. 348/349 
