The Crenation of Lipid Bilayers and of the Membrane of the Human Red Blood Cell

Abstract

Phospholipid bilayers in an aqueous medium consist of two sheets of long phospholipid molecules, the polar heads in each sheet, usually negatively charged, being in contact with the aqueous medium, and the ends of the fatty-acid chains in one monolayer lying close to the corresponding ends in the other layer (e.g.[1]). The two layers may be identical, yielding a symmetrical bilayer, or different, yielding an asymmetric bilayer. Biological membranes are usually asymmetric, and contain much non-phospholipid material such as cholesterol (which is closely associated with the phospholipid molecules) and proteins which may be disposed in various ways with respect to the two phospholipid layers. In membranes with a high metabolic activity, these proteins are abundant, and probably contribute largely to the structural properties of the membrane. The red blood cell has a very low metabolic level (MARTIN and FUHRMAN [2] show an extremely low oxygen consumption, but the red cell also performs anaerobic glycolysis), and there is only one protein molecule for every 90 molecules of phospholipid or cholesterol (though the masses of protein and lipid are roughly equal) [3(p.27), 4]. The total number of phospholipid and cholesterol molecules in one membrane is about 5 × 10⁸ (e.g.[5]). The protein spectrin, which is not found in other cells, forms some kind of network on the cytoplasmic side of the membrane [6,7].