Transmembrane movements of lipids

Abstract

Membranes allow the rapid passage of unchanged lipids. Phospholipids on the other hand diffuse very slowly from one monolayer to another with a half-time of several hours. This slow spontaneous movement in a pure lipid bilayer can be selectively modulated in biological membranes by intrinsic proteins. In microsomes, and probably in bacterial membranes, non-specific phospholipid flippases allow the rapid redistribution of newly synthesized phospholipids. In eukaryotic plasma membranes, aminophospholipid translocase selectively pumps phosphatidylserine (PS) and phosphatidylethanolamine (PE) from the outer to the inner leaflet and establishes a permanent lipid asymmetry. The discovery of an aminophospholipid translocase in chromaffin granules proves that eukaryotic organelles may also contain lipid translocators.

Sterol structure determines the separation of phases and the curvature of the liquid-ordered phase in model membranes

“…Phospholipids with their very polar headgroups flip-flop extremely slowly across the membrane (half-time of several hours; ref. 37), whereas cholesterol having as a polar group only a hydroxyl group, flip-flops moderately fast (half-time Յ 1 sec; refs. 38 and 39).…”

Phospholipids in animal eukaryotic membranes: transverse asymmetry and movement

“…More recently, the distribution of the phosphoinositides was established (Butikofer et al, 1990;Gascard et al, 1991): 100 % of the phosphatidylinositol 4-phosphate, and 80 % of the phosphatidylinositol and of its 4,5-bisphosphate derivative are located in the cytoplasmic leaflet, as is 800% of the phosphatidic acid. In fact, this distribution, with an outer surface composed principally of the choline-containing phospholipids phosphatidylcholine and sphingomyelin, seems to be a general trend for the plasma membrane of animal cells (see Table 1 and reviews by Devaux, 1992;Op den Kamp, 1979;Zachowski and Devaux, 1990). This outer monolayer is often poor in aminophospholipids, phosphatidylethanolamine and phosphatidylserine, but some plasma membranes can contain large amounts of them.…”

Partial purification and characterization of the human erythrocyte Mg2+ ‐ATPase A candidate aminophospholipid translocase

“…This transport requires the hydrolysis of cytosolic ATP [1,3,4], the presence of magnesium [5] and is inhibited by vanadate [1,5]; it is therefore a vanadate sensitive Mg-ATPase. As a consequence of the action of the aminophospholipid translocase, phospholipids are symmetrically distributed over the two membrane halves, PS and PE being located principally in the inner leaflet, while phosphatidylcholine (PC) and sphingomyelin are the main components of the outer leaflet [6]. The kinetic properties of the aminophospholipid translocase are well established, but the protein has not yet been isolated and characterized.…”