THE CYSTEINE PROTEINASES OF SCHISTOSOMA-MANSONI CERCARIAE

Based on substrate preferences, cercariae of Schistosoma mansoni were seen to express both cathepsin L and cathepsin B cysteine proteinases, although the former activity was many-fold greater. Two cathepsin L a ctivities identified in cercarial extracts by zymography co-migrated w ith activities in extracts of 3 h and 24 h schisotosomula and in extra cts of adult worms. Since these enzymes have been implicated in haemog lobin digestion by adult worms, they may perform a similar function in schistosomula. Immunolocalization using scanning electron micrographs showed that cathepsin L and cathepsin B proteinases were present in t he cercarial post-acetabular glands. In addition, cercarial serine pro teinase activities considered to facilitate skin penetration efficient ly cleaved the substrates Z-Gly-Pro-Arg-NHMec and Z-Gly-Pro-Lys-NHMec. Cercariae release most of this serine proteinase activity when induce d to secrete the contents of their acetabular glands. In contrast, new ly transformed 3 h and 24 h schistosomula did not express this activit y.