Ammonia Nitrogen Produced From Isomeric Peptides in Kidney Homogenate Digests

Abstract

On aerobic incubation of glycyl-dl-alanine and of dl-alanyl-glycine with aqueous homogenates of rat kidney tissue, considerable NH3 accumulated in digests of the former peptide, whereas little or none appeared in those of the latter. Of the isomeric tripeptides studied, only glycyl-glycyl-dl-leucine yielded NH3. The NH3 was due chiefly to d-amino acid oxidase activity and might be related specifically to the oxidative desamination of the d-amino acid moiety of the peptides. That the oxidative desamination involved the [alpha]-[beta] H atoms of the substrate was seen in the relative susceptibility of dl-valine and of dl-isovaline. The latter had a tertiary C atom. Two explanations for the behavior of the isomeric peptides were suggested: (1) d-amino acid oxidase acted only on free d-amino acids, and the NH3 could only have arisen after the action of d-peptidase on the peptides liberating the free amino acids; (2) d-amino acid oxidase acted not only on free d-amino acids, but also upon b-amino acids bound through the amino group in peptide linkage with another amino acid.