Biochemistry of Amino Acids - A. Majster 1961

The Role of Amino Acids in Nutrition
Amino Acid Antagonists
Antagonism Between Natural Amino Acids

Phenomena of antagonism between Natural Amino Acids have repeatedly been observed in studies of Bacterial Nutrition. Considerable effort has been devoted to developing "balanced media" to ensure optimal growth of microorganisms used as biological test objects. Several Examples of such antagonism can be cited. Glycine, Serine, Threonine, and ß-Alanine inhibit the growth of Streptococcus faecalis, and this inhibition can be reversed by increasing the alanine concentration in the medium [169]. A number of observations indicate antagonism between Arginine and Lysine. In a mutant strain of Neurospora crassa that has lost The ability to synthesize lysine, a competitive growth inhibition by L-arginine—absent in the original wild type—was noted, with 50% inhibition observed at equimolar concentrations of arginine and lysine in the medium [214]. On the other hand, it is known that lysine, Ornithine, and, to a lesser extent, other L-amino acids inhibit the action of arginase, whereas urea has no noticeable effect. The inhibitory effect of lysine and ornithine is reversed by arginine [182, 183]. In lactic acid Bacteria, mutual antagonism between Serine and threonine has been observed [257–259]. Similar phenomena have been described for leucine, isoleucine, and valine—a group of amino acids with a branched carbon chain [204, 205, 209, 211, 259].

Antagonism between natural amino acids has also been noted in animals. Rats fed high-leucine diets exhibited growth retardation; The addition of isoleucine to the diet partially alleviated The Effect of leucine [205]. If valine was added In addition to isoleucine, normal growth was completely restored [273]. Under appropriate nutritional conditions, antagonism can be observed between phenylalanine and isoleucine, phenylalanine and valine, and threonine and phenylalanine [273, 296]. When the protein content is increased in diets containing casein and gelatin, or casein and oxidized casein, rats develop disorders indicating an improper ratio among amino acids. The resulting growth inhibition, increased urinary Excretion of Tryptophan, and lowered plasma tryptophan levels were eliminated by the addition of tryptophan to the diet, but were not reversed by nicotinic acid [288, 297].

Thus, a series of studies points to the necessity of a specific quantitative balance among dietary amino acids. While appropriate conditions can be established experimentally to study antagonism between a specific pair of amino acids, it is highly likely that an excess of any single amino acid exerts an inhibitory effect on the METABOLISM of a whole range of Other Amino Acids. Such inhibition can be either direct (in the sense that the metabolism of a specific amino acid is disrupted) or indirect, owing to the impairment of Protein Synthesis, which requires the simultaneous utilization of many amino acids.