Growth Promotion by Invertible D-Amino Acids in Diets Containing Extraneous (Poorly Invertible) D-Amino Acids

Abstract

Excellent growth has been obtained on an L-amino acid diet containing both the essential and the non-essential amino acids. Replacement in this diet of the poorly invertible group of essential amino acids (isoleucine, leucine, lysine, threonine and valine) with their DL forms at twice the L level produced less rapid growth. The additional replacement of the readily invertible essential amino acids (arginine, methionine, histidine, tryptophan and phenylalanine) by their DL forms at the L level led to a much more marked decrease in rate of growth. In either of the two latter diets, replacement of the non-essential L-amino acids by glycine and ammonium citrate led to a further decrease in rate of gain, but their replacement by their DL isomers improved the growth response. It is therefore tentatively concluded that the D forms of the poorly invertible group of essential amino acids interfere with the inversion of the D forms of the readily invertible group. The D forms of the non-essential amino acids apparently do not augment this interference. The excellent, though not quite equal, growth obtained upon replacement of the non-essential amino acids by glycine and ammonium citrate indicates that the synthesis of the non-essential amino acids occurs surprisingly readily. The presence of the poorly invertible group of essential amino acids in the DL form at twice the L level interferes markedly with the utilization of D-histidine. This occurs not only when the latter is fed at a suboptimal level, but also when fed at a level optimal for L-histidine. The probability of interference with inversion is suggested.