CHARACTERIZATION OF THE CATHEPSIN-LIKE CYSTEINE PROTEINASES OF SCHISTOSOMA-MANSONI

Adult Schistosoma mansoni parasites synthesize and secrete both cathep sin L and cathepsin B cysteine proteinases, These cysteine proteinase activities, believed to be involved in hemoglobin digestion by adult s chistosomes, were characterized by using specific fluorogenic peptide substrates and zymography, Both cathepsin L- and B-like activities wit h pH optima of 5.2 and 6.2, respectively, predominated in soluble extr acts of worms, and both these activities were secreted by adult worms into the culture medium, The specific activity of cathepsin L was abou t double that of cathepsin B when each was assayed at its pH optimum, and moreover, the specific activities of cathepsins L and B in extract s of female schistosomes were 50 to 100% higher than in extracts of ma le schistosomes. Analysis of the primary structure of two cloned S. ma nsoni cathepsins L, here termed cathepsin L1 and cathepsin L2, reveale d that they are only 44% similar and that cathepsin L2 showed more ide ntity (52%) with human cathepsin L than with schistosome cathepsin L1, Moreover, differences in their active site, propeptide region, and po tential for glycosylation suggest separate functions for schistosome c athepsin L1 and cathepsin L2.