Effect of exogenous gangliosides on synaptosomal membrane ATPase activity

Changes in the activity of (Na+, K+)-ATPase of synaptosomal membranes induced by exogenous gangliosides were studied. Depending on the ganglioside-protein ratio, the enzyme activity was finally reduced to 40% when the ratio was about 1. By analysis of the reaction kinetics the effect was characterized as a noncompetitive inhibition. Moreover the ganglioside effect was clearly dependent on the incubation temperature. Since exogenous gangliosides thereby caused a shifting in the optimum temperature of (Na+, K+)-ATPase, the effect is discussed in terms of changes of the membrane properties. In preincubation experiments it was revealed that the interaction of the glycolipids with synaptosomal membranes itself was temperature dependent and enhanced by ATP. It is suggested that ganglioside micelles might have been incorporated by the membranes in a way comparable to a fusion process.