524 Editor: M. WINITZ 
years using the usual criterion of growth, showed a significantly greater growth response. All 
diets compared were isonitrogenous, but there were striking differences in the relative proportions 
of the essential amino acids as obtained by the fasting plasma concept and the earlier growth 
studies. A simple explanation as to why this concept is here applicable can possibly be attributed 
to the fact that since the vital body functions and metabolic processes must continue even in the 
absence of a dietary source of nitrogen, the condition found in the animal in the fasting state, 
the protein reserve of the body is broken down in the most efficient manner that will permit the 
organism to survive for the longest period of time. As the blood is the vehicle which distributes 
the amino acids liberated during this protein breakdown to the various tissues, its fasting amino 
acid composition reflects the nutritional needs of the organism. I should mention that this 
concept was not initially proposed by us but was developed by Dr. JARowsk1r of Chas. Pfizer and 
Co. Its experimental demonstration was carried out, in collaboration with members of his 
group, at our laboratory in Bethesda. This experience clearly indicated to us that the blood 
amino acid profile could tell us a good deal more about the nutritional needs and mechanisms 
of metabolic action of the organism than we had formerly thought possible. 
ROcCKLAND: It may be appropriate to recall that analogous amino acid imbalances have been 
observed with a variety of microorganisms including the lactic acid bacteria and ciliated protozoa, 
Tetrahymena. It is well known that minimal amounts of required amino acids limit the growth 
response of microorganisms in direct relation to their proportions in the basal medium and that 
under these conditions, high relative proportions of other amino acids will impose further limita- 
tions of their growth. It is perhaps more significant that even on an optimum basal medium, 
containing completely adequate amounts of required amino acids, the presence of high propor- 
tions of one or more amino acids may inhibit severely the growth response of microorganisms. 
It is suggested that the mechanisms and physiological basis for inhibited growth or other 
effects of amino acid imbalance might be elucidated through investigations of this phenomenon 
using the convenient, germ-free, one-celled animal Tetvahymena. 
SCHREIER: With this final note, we will close this session on free amino acids. Thank you very 
much, all of you. 
REFERENCES 
1E. Roperts, Intern. Symposium on Inhibition in the Nervous System and y-aminobutyric Acid, 
Pergamon Press, 1960, p. 144. 
2 R. DomMENjoz, Arch. exptl. Pathol. Pharmakol., Naunyn-Schmiedeberg’s, 208 (1948) 144. 
3 W. J. Haves, F F. FERGUSON AND J.S. Cass, Am. J. Trop. Med., 31 (1951) 519. 
4T. B. Gaines, Toxicol. Appl. Pharmacol., 2 (1960) 88. 
> B. J. Janporr, H. P. SaRETT AND O. Bopansky, J. Pharmacol. Exptl. Therap., 88 (1947) 333- 
8 J. D. Jupan, Brit. J. pharmacol., 4 (1949) 120. 
7 E. A. Hosein anp H. McLEnnNaN, Nature, 183 (1959) 328. 
8 KE. A. HOSEIN AND P. PRourx, Nature, 187 (1960) 321. 
® E. H. COLHOUN AND E. Y. SPENCER, Science, 130 (1959) 504. 
10 G.M. McKuann, R. W. ALBErRs, L. SoKoLtorr, O. MICKELSEN AND D. B. Tower, Intern. 
Symposium on Inhibition in the Nervous System and y-Aminobutyric Acid, Pergamon Press, 
1960, p. 169. 
11D. KEssEL, Federation Proc., 18 (1959) 258, A-1020. 
12 C. F. BAXTER AND E. RoBErRTS, Proc Soc. Exptl. Biol. Med., 104 (1960) 426. 
13C. F. BAxTER AND E. RosBerts, Amino Acid Pools, Elsevier Publishing Cy., Amsterdam, 
1962, p. 499. 
144 E. Roperts, in S.S. Kety anp J. ELxes, Regional Neurochemistry, Pergamon Press, 1961, 
P- 324. 
18 K. SANO AND E. Roserts, Biochem. Biophys. Research Comm., 4 (1961) 358. 
