The colorimetric determination of leucine aminopeptidase in urine and serum of normal subjects and patients with cancer and other diseases

FIRST demonstration of "leucylpepti-T dase" as a component of erepsin was made by measuring the rate of liberation of carboxyl groups from L-leucylglycine.6 However, since this substrate was hydrolyzed by enzymes other than leucylpeptidase, L-leucinamide, a more specific substrate was synthesized.' Gomori4 developed a more precise colorimetric and histe chemical method to study tissue aminopeptidase, based on the formation of azo dyes from the naphthylamine moiety liberated by enzymatic hydrolysis of glycylor alanyl-p-naphthylamide. Green et a1.6 and Folk and Burstones assayed enzymatic activity of mammalian tissues and serum by measuring the p-naphthylamine liberated by hydrolysis of L-leucyl-P-naphthylamide hydrochloride.