Identification of inhibitors of urinary alanine aminopeptidase.

Amino acids and ammonia were identified as natural inhibitors of urinary AAP. In urines from healthy volunteers approximately one half of the inhibition could be accounted for by amino acids and ammonia. At the measured concentrations, histidine, ammonia and phenylalanine, in decreasing order, were the most effective inhibitors. Results from kinetic studies with amino acids added to gel-filtered urine are consistent with the presence of two AAP isoenzymes with different inhibition characteristics. The ten amino acids which were tested show the same inhibition kinetics. Differences between amino acids are quantitative.