Structure of Biological Membranes and of Their Models. II

Abstract

For many years little attention has been paid to conclusions of the work of GORTER and GRENDAL (see Ref. 1) in 1926 that a lipid bilayer may be the major component of biological membrane. They extracted the lipids from erythrocyte membrane by an organic solvent, spread them into a monolayer the area of which at a surface pressure of 2 dyne/cm, was twice the total area of the membranes. Only in 1935 DANIELLI, when trying to elucidate the model of a biological membrane, came across this publication and was very much inspired by it. Since however, proteins comprise up to 60% of the membrane material, their configuration and their location within the membrane became the major variable in the different membrane models proposed. Membrane permeability to sugars, to phosphate and to amino acids indicated very strongly that protein molecules do not just adhere to the lipid bilayer but some of them are integral part of the membrane, spanning the lipid bilayer [1]. Thus the membrane proteins were subdivided into the water soluble peripheral (extrinsic) proteins and into the integral proteins which can be solubilized by detergents. The lateral mobility of the lipid and of the protein components of the membrane influenced the development of the fluid mosaic membrane model [2]. With the development of the fluorescence recovery after photobleaching technique it has been soon realized that a fraction of the membrane proteins has restricted mobility. The immobile membrane protein fraction could be shown to be connected to a network of proteins within the cell underneath the membrane. The fluid mosaic membrane has been modified and evidence has been gathered that the membrane shape is reinforced and shaped by the cytoskeleton exerting also control on the location and the movement of the different membrane proteins performing specific functions [3]. Here I wish to discuss the possible molecular configurations of the lipids and of the proteins and their interrelation with the different intermolecular interactions, will be discussed.