Cell membranes

Abstract

A critical evaluation is presented on investigations on the reaggregation of lipids and proteins of cell membranes and also studies postulating the various models of the globular organization of cell membranes. On the basis of a brief discussion of our experiments on the ultrastructure of the membranes of the mitochondria, photoreceptors, erythrocytes, myelin and lipoprotein models and comparison of these results with the findings of other investigations carried out by methods of X-ray structural analysis (x.s.a.), electron microscopy (e.m.) nuclear magnetic resonance (n.m.r.), electron paramagnetic resonance (EPR) methods of the spin label (spin-tag) and scanning calorimetry, the method of freeze etching etc., the general scheme of the molecular organization of cell membranes is postulated. The structural stabilization of the membranes must come about from association of the glycolipid and sialo glycoprotein complexes and also near-membrane and membrane proteins with polar and fatty acid regions of lipid molecules. The fatty acids of the membrane lipids and glycolipids form a continuous bimolecular fatty acid "carcass" of the cell membranes possessing high ohmic resistance. The protein sub-particles isolated from convex and concave etchings of frozen membranes must be situated not at the centre of the lipid bilayer but in its interphasic regions. Associating electrostatically and hydrophobically with certain phospholipids these sub-particles may determine the specific properties of the membranes and their individual regions (synaptic contacts, etc.). The regions of the protein sub-particles partially buried in the lipid layer may possess opposite properties in relation to the regions of the same protein sub-particles present in hydrophilic surroundings. In hydrophilic and interphasic regions of the membranes low molecular weight protein and glycoprotein molecules may be present between the protein sub-particles. These molecules must have "free" association with each other and with the hydrophilic regions of the protein sub-particles. Such complexes may have a fibrillar structure and a honeycomb organization. Of great importance in the functioning of the membranes is structured water. On the basis of the postulated structural organization an attempt is made to explain certain functional characteristics of cell membranes. © 1972.