MANIPULATION OF THE PHOSPHATIDYLETHANOLAMINE POOL IN THE HUMAN RED-CELL MEMBRANE AFFECTS ITS MG2-ATPASE ACTIVITY()

Decreasing the size of the outer leaflet pool of phosphatidylethanolam ine (PE) in the erythrocyte membrane by treatment of intact cells with either phospholipase A(2) or trinitrobenzenesulphonic acid (TNBS), ca uses a corresponding decrease in Mg2+-ATPase activity as determined in their respective ghosts. Also, incubation of ghosts with Ro09-0198, a cyclic peptide from Streptoverticillium which is known to interact sp ecifically with PE, causes a decrease in Mg2+-ATPase activity which is dependent on the amount of peptide added. These three different appro aches, all causing a decrease in endogenous PE, thus result in a conco mitant decrease in Mg2+-ATPase activity which reaches a plateau level at approximately 25% residual activity. Hence, it is inferred that the complementary fraction (75%) of the total Mg2+-ATPase in the red cell membrane is closely related to the functioning of its aminophospholip id specific translocase as it mediates a (continuous) transport of PE molecules from outer to inner membrane leaflet. This view is supported by the observation that an increase in the total amount of PE in the membrane by decarboxylation of an appreciable fraction of its PS, resu lts in a considerable increase in Mg2+-ATPase activity.