Red blood cell biomembrane structure and deformability

Abstract

The red blood cell membrane is built upon a phospholipid bilayer matrix. The lipid classes are asymmetrically distributed with the lecithins and sphingomyelins arranged on the outside of the membrane whereas the phosphatidy-lethanolamines and phosphatidylserine lipids are on the inside surface of the cell (Bretscher, 1973). The membrane contains considerable amounts of cholesterol which therefore has an important control on the lipid fluidity. Both intrinsic and extrinsic proteins occur. Major constituents are spectrin and band 3. Band 3 consists of hydrophobic proteins which span the membrane, have a molecular weight of 90 000 and comprise about 24% of the total membrane protein (Steck, 1974). The major glycoprotein also spans the membrane. Glycophorin and band 3 proteins are thought to constitute the particles seen in freeze fracture electron microscopy. Recently great attention has been focused on the red cell membrane skeleton. Spectrin is the major skeletal protein (60–75% by weight) and is composed of two sub-unit bands of molecular weight 240,000 and 220,000 (Guidotti, 1972). Purified spectrin heterodimers and heterotetramers have been isolated and studied. Various complexes with actin and with ankyrin have been postulated. Models have been proposed of how skeletal proteins are arranged with respect to the lipid bilayer matrix (Lux, 1979). Some workers suggest that the flexibility, deformability and durability of red blood cells is dependent upon this membrane skeleton and furthermore that defects in the structure are perhaps responsible for a number of haemolytic anaemias. In this talk we will examine and discuss the present evidence of the structure of red blood cell biomembranes, its membrane skeleton and the potential for deformability of this structure.