Acidic thiol proteinase activity of Schistosoma mansoni egg extracts

Extracts of the eggs of the human blood fluke, Schistosoma mansoni, exhibit proteolytic activity which requires the presence of added thiol reagents or cyanide. The pH optimum for hydrolysis of Azocoll and cartilage proteoglycan is 4.8--5.2 and the molecular weight of the major component is 25--26,000. The effects of inhibitors suggest this activity belongs to the acidic thiol proteinase class, with a similarity to Cathepsin B. These proteinases may be involved in nutrition of the egg or sporocyst, in penetration of eggs or miracidia through host tissues, or in the immunopathology of schistosomiasis.