A FLUID LIPID-GLOBULAR PROTEIN MOSAIC MODEL OF MEMBRANE STRUCTURE.

The thermodynamic and experimental bases for the lipid-globular protein mosaic model for the organization of biological membranes, which was proposed some six years ago (Lenard and Singer, 1966) and has since been elaborated are described. In this model, the integral proteins of membranes are postulated to have an amphipathic structure in the intact membrane; that is, their ionic and highly polar groups are largely located on the membrane surfaces in contact with the aqueous medium, while their nonpolar residues are sequestered from contact with water in the membrane interior. These proteins are intercalated into a discontinuous lipid bilayer in this model. Recent experimental results are consistent with the suggestion that the lipid forms the matrix of the mosaic, and since the membrane lipid is generally fluid rather than crystalline under physiological conditions, the mosaic is expected to be a dynamic one. That is, the membrane appears to be a two-dimensional viscous solution, with its components able to undergo translational diffusion in the plane of the membrane. Some of the many important functional and physiological corollaries of this structural hypothesis are discussed.