An elastase-like proteinase was localized histochemically in the penetration glands of the cercariae of Neoglyphe sobolevi. The enzyme extracted from the larvae hydrolyzed azocoll, gelatin, azoalbumin, azocasein, and elastin-orcein at optimal pH of 8.4, 8.4, 8.0, 7.6, and 8.4, respectively. The nonionic detergent Triton X-100 slightly enhanced its activity toward azocoll, whereas the anionic detergent SDS, and the cationic detergent cetyltrimethylammonium bromide acted as strong inhibitors. Magnesium ions stabilized the proteinase activity. Strong calcium and magnesium chelators (EGTA, EDTA) and the serine proteinase inhibitor DFP (0.1 mM) inhibited it. 2 mM 1,10-phenanthroline, a relatively specific chelator of zinc, produced a weak inhibition. The results indicate, therefore, that the active proteinase represents a metal-enzyme complex rather than a metalloenzyme. Being capable of hydrolyzing N-blocked L-alanine-1-naphthylester, N-blocked L-methionine-1-naphthylester, and naphthyl AS-D chloroacetate at pH 6.8, the proteinase activity was insensitive to 1 mM p-nitrophenyl phosphate, an inhibitor of some mammalian esterproteinases. The enzyme did not split N-blocked-DL-phenylalanine-2-naphthylester and also N-blocked L-aminoacyl- and N-blocked L-peptidyl-naphthylamides bearing L-arginine, L-alanine, L-phenylalanine, L-leucine, or L-proline at the P₁ subsite. At operative pH values of 4.8 and 3.5 generated during electrophoresis in a stacking and a resolving gel, respectively, the cercarial proteinase migrated toward the cathode. The separated enzyme produced four bands of proteolysis in a gelatin-containing polyacrylamide gel, at the optimal pH of 8.4.
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