Hereditary spherocytosis (HS) is a congenital haemolytic anaemia which is characterized by a great variety of structural defects in the red cell's membrane skeleton and/or deficiencies in particular membrane (skeletal) proteins. Enhanced (Mg2+)-dependent adenosine triphosphatase (Mg(2+)-ATPase) activities, varying from 115% to 160%, were invariably found in erythrocyte ghosts derived from 13 HS patients. Similarly, an enhancement of Mg(2+)-ATPase activity by 30% is observed in normal red cell ghosts that have been stripped of the greater part of their membrane skeletal proteins by treatment with a low ionic strength buffer. Reassociation of those stripped ghosts with spectrin reduces the enhanced Mg(2+)-ATPase activity to its original level. Since in both cases, HS ghosts and stripped normal ghosts, the stabilizing effects that the membrane skeleton exerts on the maintenance of an endofacial localization of the aminophospholipids are impaired, the enhanced Mg(2+)-ATPase activity is interpreted to reflect an increased activity of the aminophospholipid translocase. The present observations therefore support a role of the membrane skeleton in the stabilization of phospholipid asymmetry in the red cell membrane and consequently in reducing the energy consumption of the translocase.
Decreasing the size of the outer leaflet pool of phosphatidylethanolamine (PE) in the erythrocyte membrane by treatment of intact cells with either phospholipase A2, or trinitrobenzenesulphonic acid (TNBS), causes a corresponding decrease in Mg(2+)-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 specifically with PE, causes a decrease in Mg(2+)-ATPase activity which is dependent on the amount of peptide added. These three different approaches, all causing a decrease in endogenous PE, thus result in a concomitant decrease in Mg(2+)-ATPase activity which reaches a plateau level at approximately 25% residual activity. Hence, it is inferred that the complementary fraction (75%) of the total Mg(2+)-ATPase in the red cell membrane is closely related to the functioning of its aminophospholipid 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, results in a considerable increase in Mg(2+)-ATPase activity.
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