The Aminophospholipid Transporter from Human Red Blood Cells

Abstract

Nearly twenty years ago, Bretscher (1972) proposed that the distribution of phospholipids in the erythrocyte membrane is asymmetric. It is now well established that certain phospholipids preferentially reside in either the inner or outer membrane leaflets of most cell types. For example, phosphatidylcholine and sphingomyelin are predominantly localized in the plasma membrane’s outer leaflet, while phosphatidyl inositol and the aminophospholipids, phosphatidylethanolamine (PE) and phosphatidyl serine (PS), are primarily localized in the inner leaflet (Gordesky et al., 1975; Verkleij et al., 1973). Recent studies have provided convincing evidence that membrane lipid asymmetry is generated and probably maintained by specific transport proteins or ‘flippases’ (Backer and Dawidowicz, 1987; Bishop and Bell, 1985). One of these transport proteins, the aminophospholipid transporter, is responsible for the movement of PS and PE from the outer leaflet to the inner leaflet of the erythrocyte membrane (Seigneuret and Devaux, 1984; Daleke and Huestis, 1985; Tilley et al., 1986; Connor and Schroit, 1987).