Properties and drug sensitivity of adenosine triphosphatases from Schistosoma mansoni

The hydrolysis of ATP was measured in the presence of schistosome homogenates and various cations. The enzyme was stimulated strongly by either Ca2+ or Mg2+. Na+ added to the activation by Ca2+. A minor (17%) component was Na+ + K+ + Mg2+-dependent and ouabain-sensitive. Praziquantel, niridazole, oxamniquine, and hycanthone had no direct effect on the ATPase activity of schistosome homogenates. When schistosomes were pretreated with these drugs in vitro, washed thoroughly, and then homogenized, hycanthone, praziquantel, and oxamniquine caused a reduction in ATPase content of the worms. Niridazole did not share this effect. These results suggest that antischistosomal drugs did not directly inhibit ATPase, but did reduce ATPase in whole worms, possibly by removing or damaging the tegument, which is thought to contain most of the ATPase activity. In vitro ATPase measurements may be a useful indicator of pharmacologic activity of some types of drugs.