The chymotrypsin-like activity of human prostate-specific antigen, γ-seminoprotein

γ-Seminoprotein (γ-Sm) is a human prostate-specific antigen and a serine protease judging from the complete amino acid sequence which shows extensive homology with the kallikrein family. The enzymatic activity of γ-Sm was defined as a chymotypsin-like activity using reduced and S-3-(trimethylated amino)propylated lysozyme and insulin-oxidized A and B chains as substrates. The -Leu↓Ser- peptide bond of lysozyme was rapidly hydrolyzed by γ-Sm. γ-Sm also hydrolyzed the -Phe↓Glu- of lysozyme and the -Leu↓Cys(SO3H) -of insulin B chain. Insulin A chain and arginyl- or lysyl-linkage of these proteins were not hydrolyzed by γ-Sm at all.