Effect upon Growth of the D Isomers in Synthetic Mixtures of the Essential Amino Acids

Publisher Website
Google Scholar
Abstract
Rats fed suboptimal percentages of the 10 essential amino acids as the chief source of dietary nitrogen grew somewhat better when the poorly invertible group of essential amino acids (valine, leucine, isoleucine, lysine and threonine) was supplied in the DL form at twice the L level. Presumably the extraneous D-amino acids provide nitrogen for limited synthesis of the non-essential amino acids, though much less readily than do even smaller amounts of glycine and ammonium citrate. When the group of amino acids, whose D modifications are readily invertible (tryptophan, methionine, phenylalanine, histidine and arginine) when each is fed singly, were all fed simultaneously in the DL form in amounts calculated to provide adequate amounts of each L form after inversion somewhat slower growth occurred at the basic 5.9% level than when the diet contained these amino acids in the L form only. Less growth was attained when this group of amino acids was supplied only in the D form, and increasing the allotment of these D-amino acids as a group did not increase the rate of growth. In analogous tests at a basically lower (2.95%) dietary level, growth when this group of amino acids was supplied in the DL form was about the same as when the group was fed in the L form. When the readily-invertible group was provided only as D-amino acids, the growth response was poorer, but it improved with increase in allotment. Failure of the D forms of the invertible group to promote as rapid growth as in the L controls can be attributed largely to incomplete or to slow inversion. Failure to increase the rate of growth at the higher dietary levels by increasing the allotment of the readily invertible D-amino acids suggests that a ceiling is imposed on the overall capacity of the animal to effect stereonaturalization en masse of the D-amino acids whose inversions singly occur readily. Reasons for making this assumption are discussed.

This publication has 17 references indexed in Scilit: