AMINOPHOSPHOLIPID TRANSLOCASE AND PROTEINS INVOLVED IN TRANSMEMBRANE PHOSPHOLIPID TRAFFIC

The transmembrane distribution of phospholipids in the membranes of eu karyotic cells depends on specific proteins (called flippases). The am inophospholipid translocase is responsible for the sequestration of ph osphatidylserine and phosphatidylethanolamine in the cytosolic leaflet of plasma membranes. Several laboratories are presently working on th e identification, purification and cloning of this Mg-ATPase, first re cognized in the human red cell membrane. In accordance with the 1992 h ypothesis of Higgins and Gottesman, proteins of the MDR1 family appear to be able to translocate certain phospholipids from the inner to the outer monolayer of the plasma membrane. It has been reported in parti cular that expression of the human MDR3 and mouse mdr2 genes promote t ranslocation of long chain phosphatidylcholine, while expression of th e MDR1 gene stimulates the outward motion of phospholipids possessing at least one short chain. ATP-independent flippases activities were re cognized not only in microsomes but also in Golgi membranes. (C) 1997 Elsevier Science B.V.