A Mg2+-independent Ca2+-stimulated ATPase activity in the tegument of Schistosoma mansoni.

A tegumental fraction was prepared from Schistosoma mansoni. This fraction exhibited ATPase activity stimulated by Ca2+ in the absence of Mg2+. The Mg2+ independency was assessed by lowering contaminant Mg2+ using CDTA. The peak of activity was 220 mumol Pi mg-1 protein h-1 and the K0.5 for CaATP was 0.32 mM; the same K0.5 was obtained using MgATP as substrate, in the absence of Ca2+. Both activities may be promoted by the same enzyme since the addition of Ca2+ did not increase the ATPase activity measured in the presence of a saturating MgATP concentration.