THE EFFECT OF ETHANOL ON THE PLASMA-MEMBRANE CALCIUM-PUMP IS ISOFORM-SPECIFIC

The effect of ethanol has been studied on four different isoforms of t he plasma membrane Ca2+-ATPase expressed in Sf9 cells with the help of the baculovirus system. The PMCA2CI protein was maximally activated b y 0.5% ethanol, a concentration 8-10 times lower than that needed to o btain the same effect on the PMCA4 protein or on the pump of erythrocy te membranes, which is a mixture of isoforms 1 and 4. Experiments perf ormed with truncated pumps indicated that the stimulation by ethanol w as lost if the C-terminal region between Lys(1065) and Lys(1161), enco mpassing the calmodulin binding domain, was removed. These observation s indicate that the stimulation is the result of a direct interaction of ethanol with the C terminal regulatory domain of the Ca2+ pump.