Proteinase activity in miracidia, transformation excretory-secretory products, and primary sporocysts of Schistosoma mansoni.

Proteinase activity was detected in the culture medium of transforming miracidia and in detergent extracts of Schistosoma mansoni miracidia and primary sporocysts using a fluorescent substrate, carbobenzoxy-phenylalanyl-arginyl-7-amino-4- trifluoromethylcoumarin. Medium collected after the first 24 hr of miracidial cultivation (transformation medium; TM) contained most (80%) of the activity released during 5 days of in vitro culture. Based on proteinase activity contained in Triton X-100 extracts of whole larvae, miriacidia and primary sporocysts exhibited a similar amount of total activity per organism, whereas specific activity was about 2-fold greater in miracidia. Approximately 10% of total miracidial activity was released during the first 24 hr of transformation. This early release of proteinase is consistent with possible involvement of these enzymes in miracidial snail penetration. Proteinase activities from larval extracts and culture media were identical when characterized for thiol-dependence, inhibitor profile, and pH optimum and indicate that the proteinase(s) belongs to the cysteine class of acidic endopeptidases. Further studies with TM revealed a substrate preference for a hydrophobic amino acid in the P2 position. High performance liquid chromatography gel filtration showed 2 peaks of activity at 19,000 and 36,000 Da, whereas specific inhibitor labeling yielded heterogeneous banding in the molecular weight range of 33,000-44,000 Da. Lastly, sporocyst extracts incubated with snail plasma (cell-free hemolymph) revealed degradation of high molecular weight hemolymph proteins, including hemoglobin. The finding of significant cysteine proteinase activity in miracidia and primary sporocysts and the continued low level of secretion by sporocysts suggest a functional role of these proteinases in the establishment and/or maintenance of infections within the snail host.