Properties of a series of tegumental membrane-bound phosphohydrolase activities of Schistosoma mansoni

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Abstract
Incubation of S. mansoni for 5 min in a phosphate-buffered medium, pH 7.4, released tegumental material containing the following phosphohydrolase activities: alkaline phosphatase, 5''-nucleotidase, glycerol-2-phosphatase, glucose-6-phosphatase, phosphodiesterase and ATPase. Maximum activity of these enzymes was measured at pH 9.5; the phosphodiesterase and ATPase activities were also appreciable at pH 7.0.3. Solubilization of the released tegumental material in 1% Triton X-100 followed by gel filtration distinguished 3 peaks of enzyme activity: an ATPase (MW > 1,000,000), a phosphodiesterase (MW 1,000,000) and an alkaline phosphomonoesterase with broad specificity (MW 232,000). The ATPase activity was highly activated by 10 mM-Mg2+ or 1 mM-Ca2+ and was inhibited by chelating agents. Ouabain, Na+ and K+ had little effect on enzyme activity; activity was increased by 50% in the presence of calmodulin. The phosphodiesterase activity was highest in the presence of 100 mM-Na+ or -K+, and 10 mM-Mg2+ or -Ca2+. Alkaline phosphatase activity also was stimulated by 100 mM-Na+ or -K+ and 10 mM-Mg2+; Ca2+ inhibited at > 1 mM. Surface iodination of parasites followed by detergent solubilization and gel filtration of the released tegumental membranes indicated that these enzymes were inaccessible. A major surface component, apparent MW 80,000, was iodinated. Rabbit anti-(mouse liver 5''-nucleotidase) antibodies did not inhibit the phosphohydrolase activities. An immunoglobulin G fraction from sera of mice chronically infected with S. mansoni partially inhibited alkaline phosphatase activity, but was without effect on the phosphodiesterase and ATPase activities. The location of the enzymes in the double membrane of the tegument and their significance in host-parasite interactions is discussed.