The lipids of red cell membranes: Compositional, structural and functional aspects

Abstract

The structural matrix of the erythrocyte membrane is provided by a lipid bilayer containing more than one hundred different molecular species of lipid. The phospho- and glycolipids are distributed over the two halves of the bilayer in a highly asymmetric fashion; the outer monolayer consisting of all the glycolipids and the greater part of the two choline-containing phospholipids, whereas the amino-containing phospholipids dominate the inner monolayer. Functional implications of this arrangement are still poorly understood, but some of them may be found in blood coagulation and lipid-requiring membrane-bound enzymes.

The bilayer exhibits a high degree of stability as is illustrated by ³¹P-NMR studies of membranes treated with phospholipases. However, selective modification of the molecular species of lecithin in the outer monolayer may lead to such destabilizations that the structural integrity of the membrane is lost and the cells haemolyse.

Key Words:

• asymmetry
• blood coagulation
• cation-transporting ATPases
• phos-pholipid exchange protein
• ³¹P-NMR