ATP-dependent asymmetric distribution of spin-labeled phospholipids in the erythrocyte membrane: relation to shape changes.

TLDR

Spin‑labeled analogs of phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine have been used to study phospholipid transverse diffusion and asymmetry in the human erythrocyte membrane. The study proposes that ATP‑driven transport of amino phospholipids to the inner leaflet underlies membrane asymmetry and explains the ATP requirement for maintaining the erythrocyte discoid shape. Transbilayer distribution of spin‑labeled phospholipids was assessed by ascorbate reduction. Initially all three spin‑labeled phospholipids entered the outer leaflet, and at 5 °C phosphatidylcholine remained outer while phosphatidylserine and phosphatidylethanolamine rapidly translocated to the inner leaflet, a redistribution that was reversible upon ATP depletion and could be reproduced in resealed ghosts only with Mg‑ATP.

Abstract

Spin-labeled analogs of phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine have been used to study phospholipid transverse diffusion and asymmetry in the human erythrocyte membrane. Ascorbate reduction was used to assess the transbilayer distribution of the labels. All three spin-labeled phospholipids initially incorporated into the outer leaflet of the membrane. On fresh erythrocytes at 5 degrees C, the phosphatidylcholine label remained mainly in the outer leaflet. In contrast, the phosphatidylserine and phosphatidylethanolamine labels underwent rapid transverse diffusion that led to their asymmetric distribution in favor of the inner leaflet. The latter effect was reversibly inhibited after ATP depletion of the erythrocytes and could be reproduced on resealed erythrocyte ghosts only if hydrolyzable Mg-ATP was included in the internal medium. It is suggested that an ATP-driven transport of amino phospholipids toward the inner leaflet could be the major cause of the phospholipid asymmetry in the erythrocyte membrane. It is also proposed that the same mechanism could explain the ATP requirement of the maintenance of the erythrocyte membrane discoid shape.