The interaction of ethanol with reconstituted synaptosomal plasma membrane Ca2+ -ATPase

The primary effect of ethanol is on the central nervous system. However, the molecular mechanisms responsible for the physiological symptoms of ethanol intoxication are still unknown. Low concentrations of ethanol were observed to stimulate the activity of the calcium pump from reconstituted synaptosomal plasma membrane Ca2+ -ATPase (PMCA), and ethanol inhibited Ca2+ -ATPase activity at concentrations above 5%. The greatest stimulating effect was obtained with 5% (v/v) ethanol and was lipid-dependent, being 74% when the protein had been reconstituted in phosphatidylcholine (PC) and less when the reconstituted protein had previously been activated by calmodulin or after removal of a 9-kDa autoinhibitory site by controlled trypsinization. Stimulation of the pump by ethanol was lower for the native or trypsin-digested protein in the presence of phosphatidylserine than in PC. These results suggest a direct ethanol-protein interaction, because the activating effect depended on the state of Ca2+ -ATPase (native or truncated, or in presence of calmodulin). The activating mechanism of ethanol may involve opening an autoinhibitory domain located close to the calmodulin binding domain.