A protocol for Leuconostoc oenos plasma membrane isolation, which was improved for studying lipidic and proteic constitution according to growth conditions, allowed us to determine some kinetic properties of membrane-bound ATPase activity : optimum pH, 5.6; the Michaelis constant (K-m) for ATP, 1.1 mM; Mg2+-dependence. L. oenos membrane-bound ATPase activity was regulated according to cell growth phase, growth medium and extracellular conditions. The regulation mode of this activity was not investigated but it was very rapid : differences in level of activity were observed in less than Ih when extracellular pH was modified or when ethanol was added. Wine induced a large decrease in ATPase activity of L. oenos. This may explain the loss of cell viability after direct inoculation into wine, when malolactic fermentation was not spontaneously obtained.