Antagonism of Poorly Invertible D-Amino Acids Toward Growth Promotion by Readily Invertible D-Amino Acids

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Abstract
Replacement of L-histidine by D-histidine in purified L-amino acid diets promotes appreciably less rapid growth, particularly when the histidine is fed at one-half the normal level. At this level, the response to the D-histidine is almost completely inhibited by including the poorly invertible D-forms of lysine, threonine, isoleucine, leucine, and valine in the diet. The antagonism is not attributable uniquely to any single D-amino acid, but appears rather to be cumulative. Qualitatively the same en masse effect of the D-forms of this poorly invertible group of the essential amino acids could be demonstrated toward the growth promotion by one-half normal levels of the other readily invertible D-amino acids tested (D-methionine, D-phenylalanine, and D-tryptophan). The quantitative variations in response noted probably reflect differences in dietary concentration of the readily invertible D-amino acids tested and differences in their normal susceptibilities to attack by D-amino acid oxidase.