ABSTRACT
This chapter shows that the duality of membrane dynamics is apparent in protein lateral mobility and makes it necessary to visualize cell membranes as fluid-solid composites. The plasma membrane of many cells may feature on its cytoplasmic face a relatively stable and static protein network, the membrane skeleton. A more fluid lipid bilayer containing embedded proteins, attached to the membrane skeleton on its external face, is an element common to most cellular membranes. Hormone-sensitive adenylate cyclase is a molecular machinery which receives, transduces, amplifies, and translates the hormonal signal at the level of the plasma membrane. The restriction of protein lateral mobility in the erythrocyte membrane is clearly related to the membrane skeleton. Many membrane functions require a certain degree of protein mobility which is met by the measured diffusion coefficients. Integral membrane proteins frequently have large portions extending into the aqueous phase.
