In order to understand the fluid nature of biomembrane, which plays crucially important role in many aspects of life phenomena, the molecular motion of phospholipid and membrane protein is discussed in this review. It is shown that the primary determinant for the fluidity in the lipid bilayer and the rate for diffusive motion of lipid and protein molecules is the width and rate of wobbling motion of phospholipid acyl-chain in the nanosecond time region. For the lateral and rotational diffusion rate of membrane proteins, however, interaction between protein and cytoskeleton is also important as the secondary determinant. The rate of segmental motion of protein is partly governed by the surrounding phospholipid species, suggesting that specific phospholipids support the optimum conditions in protein structure to develop its action.
Consequently, the term “membrane fluidity” is complex conception having a hirarchical structure which consists of lipid and protein molecules.
