D-Aspartyl residue in a peptide can be liberated and metabolized by pig kidney enzymes

The presence of an enzyme activity which hydrolyzes glycyl-D-aspartate was found in the homogenates of pig kidney cortex. The activity was inhibited by metal chelating agents and cilastatin, suggesting that the enzyme was a cilastatin-sensitive metallo-peptidase. Of the two hydrolysis products,D-aspartate was found to be less accumulated than glycine. The fate ofD-aspartate was, therefore, examined and the amino acid was found to be converted toL-aspartate,L-alanine and pyruvate, in the presence ofL-glutamate. Experiments with enzyme inhibitors suggested that the conversion involvedD-aspartate oxidase, aspartate aminotransferase and alanine aminotransferase as well as decarboxylation of oxaloacetate produced fromD-aspartate. All the results indicate that the enzymes in the pig kidney can liberate theD-aspartyl residue in the peptide and convert it to the compounds readily utilizable. The finding suggests a probable metabolic pathway of theD-aspartate-containing peptide.