HIGH-AFFINITY CALCIUM-STIMULATED, MAGNESIUM-DEPENDENT ADENOSINE-TRIPHOSPHATASE IN TRYPANOSOMA-CRUZI

1. A high-affinity (Ca2+ + Mg2+)-ATPase and a low-affinity Mg2+-ATPase were identified in the 105,000 g fraction from epimastigote forms of Trypanosoma cruzi, the agent of Chagas' disease (Tulahuen strain). 2. Activities were conserved after enzyme solubilization with deoxycholate. 3. The Ca2+-stimulated ATPase activity was (a) lower than that of the Mg2+-ATPase; (b) inhibited by p-chloromercurobenzoate and orthovanadate and (c) insensitive to oligomycin. 4. Optimal stimulation by Ca2+ was observed at pH 6.5-6.8 in the presence of 1 mM MgCl2 and 0.1 M KCl. 5. The Mg2+-ATPase was insensitive to p-chloromercurobenzoate and orthovanadate and did not require KCl for activity. 6. Kinetic analysis of the (Ca2+ + Mg2+)-ATPase yielded a half-maximal stimulating concentration of 1.1 muM for Ca2+ and a K(m) of 66 muM for ATP. 7. The (Ca2+ + Mg2+)-ATPase clearly differed from the Ca2+- or Mg+-ATPases previously characterized in the same strain of T cruzi (Frasch et al., 1978; Comp. Biochem. Physiol. 60B, 271 275).