Biochemical comparison of the serine protease (elastase) activities in cercarial secretions from Trichobilharzia ocellata and Schistosoma mansoni
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We report on serine protease activity in cercarial secretions (CSs) from the bird parasite Trichobilharzia ocellata. Using a colorigenic substrate, the biochemical properties of this enzyme were studied and its activity was compared to the homologous one in CSs from the human parasite Schistosomamansoni. The specific serine protease activity was always 2- to 3-fold higher in CSs from T. ocellata compared to S. mansoni. The enzyme has its optimal activity at pH 10.5, is Ca2+-dependent (inhibition with EDTA) and has a trypsin-like (inhibition with anti-pain) serine proteinase activity (inhibition with PMSF and aprotinin). The Km value of the serine protease from T. ocellata was higher than that of S. mansoni, and the Ki values for several inhibitors were generally lower for the enzyme of T. ocellata than that of S. mansoni except for EDTA. The enzyme activities from both parasites had a molecular weight of 30 kDa in gelatin-SDS-polyacrylamide gels. The intensity of the gelatin digestion bands was stronger with the T. ocellata than with the S. mansoni enzyme.
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