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The effect of ethanol has been studied on four different isoforms of the plasma membrane Ca 2؉ -ATPase expressed in Sf9 cells with the help of the baculovirus system. The PMCA2CI protein was maximally activated by 0.5% ethanol, a concentration 8 -10 times lower than that needed to obtain the same effect on the PMCA4 protein or on the pump of erythrocyte membranes, which is a mixture of isoforms 1 and 4. Experiments performed with truncated pumps indicated that the stimulation by ethanol was lost if the C-terminal region between Lys 1065 and Lys 1161 , encompassing the calmodulin binding domain, was removed. These observations indicate that the stimulation is the result of a direct interaction of ethanol with the C-terminal regulatory domain of the Ca 2؉ pump.

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Despite previous reports [McLaughlin (1985) Mol. Biochem. Parasitol. 15, 189-201; Ghosh, Ray, Sarkar and Bhaduri (1990) J. Biol. Chem. 265, 11345-11351; Mazumder, Mukherjee, Ghosh, Ray and Bhaduri (1992) J. Biol. Chem. 267, 18440-18446] suggesting that the plasma-membrane Ca(2+)-ATPases of different trypanosomatids differ from the Ca2+ pumps present in mammalian cells, Trypanosoma cruzi plasma-membrane Ca(2+)-ATPase shares several characteristics with the Ca2+ pumps present in other systems. This enzyme could be partially purified from epimastigote plasma-membrane vesicles using calmodulin-agarose affinity chromatography. The activity of the partially purified enzyme was stimulated by T. cruzi or bovine brain calmodulin. In addition, the enzyme cross-reacted with antiserum and monoclonal antibody 5F10 raised against human red-blood-cell Ca(2+)-ATPase, has a molecular mass of 140 kDa and forms Ca(2+)-dependent hydroxylamine-sensitive phosphorylated intermediates. These results, together with its high sensitivity to vanadate, indicate that this enzyme belongs to the P-type class of ionic pumps.