ABSTRACT
For the past twenty years the predominant concept of membrane organization has been embodied in the fluid mosaic model. A popular rendering of this model envisions the lipid bilayer acting as a matrix in which a veritable vegetable garden of membrane proteins are situated, some of whose roots penetrate and pass through the bilayer. The principal obstacle to identifying domains in membranes is that many techniques measure overall or average membrane properties. Dealing with biological membranes as having a “bulk membrane viscosity” is an oversimplification. Rather, the membrane appears to be organized into microenvironments or domains of nonaverage composition and physical properties. Physiological transformations appear to manifest themselves, not as changes in bulk membrane fluidity, but, as changes in the ensemble of membrane domains. Spectroscopic probes selectively partition between these domains and can be used to monitor specific membrane domains.
