Techniques to Determine Transbilayer Organization and Dynamics of Membrane Phospholipids

Abstract

Nowadays, there are no more arguments opposing the view that the structural backbone of a biological membrane is provided by a lipid bilayer, the fatty acyl chains of the phospholipids forming the hydrophobic core of the membrane and their polar head groups facing the aqueous environments at either side of the bilayer. As a consequence of the primary task of a membrane, which is to separate two aqueous compartments from one another in which entirely different processes take place, it is conceivable that the chemical characteristics of one side of a membrane differ considerably from those of the other. Indeed, the absolute asymmetry in both transversal localization and orientation of, respectively the periferal and integral, proteins in a membrane has already been recognized a couple of decades ago. Since the early seventies, it is also known that the different classes of phospholipids may be distributed over both halves of the bilayer in a highly asymmetric fashion, which phenomenon particularly applies to plasma membranes. The first information on this point has been gained from studies on erythrocytes and, still, the membrane of those cells is the best characterized one with regards to the transbilayer organization and dynamics of its lipids (Op den Kamp, 1979).