A SERINE PROTEINASE IN THE PENETRATION GLANDS OF THE CERCARIAE OF PLAGIORCHIS ELEGANS (TREMATODA, PLAGIORCHIIDAE)

Cercariae of Plagiorchis elegans secrete a serine proteinase from thei r penetration glands. The enzyme hydrolyzes both azocoll and, gelatin at the optimal pH of 8.4 but is incapable of hydrolyzing elastin at th e pH range of 7.2-10.0 Ca2+ and Mg2+ activate it, whereas metal chelat ors (1 mM EGTA, 1 mM EDTA) and serine proteinase inhibitors (1 mM PMSF and 0.1 mM DFP) act as strong inhibitors. The proteinase activity is insensitive to thiol-blocking compounds and to 5 mM 1,10-phenanthrolin e, a relatively specific chelator of zinc. It appears, therefore, that the active proteinase represents a metal-enzyme complex rather than a metalloenzyme. Being capable of hydrolyzing M-blocked L-alanine-1-nap hthylester, N-blocked L-methionine-1-naphthylester, and naphthyl AS-D chloroacetate at pH 6.8, the proteinase is insensitive to 1 mM p-nitro phenyl phosphate, an inhibitor of some mammalian esterproteinases. The enzyme does not split N-blocked DL-phenylalanine-2-naphthylester, non specific esterase substrates (I-naphthyl acetate, 1-naphthyl butyrate, 5-bromoindoxyl acetate), or several N-blocked L-aminoacyl- and N-bloc ked L-peptidyl-naphthylamides bearing L-arginine, L-alanine, L-phenyla lanine, L-leucine, or L-proline at the P-1, subsite. At operative pH v alues of 4.8 and 3.8 generated during electrophoresis in a stacking an d a resolving gel, respectively, the cercarial proteinase migrates tow ard the cathode. The separated enzyme produces three bands of proteoly sis in a gelatin-containing polyacrylamide gel at the optimal pH of 8. 4. The presence of the proteinase in the penetration glands, in the se cretory canals, and in the secretion from the glands suggests that the enzyme facilitates penetration, thus enabling the larvae to force the ir way through tissues of their hosts.