Proteins integral rotational diffusion

L. I. Horvath, T. Heimburg, P. Kovachev, J. B. C. Findlay, K. Hideg, D.Marsh, Integration of a K+ channel-associated peptide in a lipid bilayer Conformation, lipid-protein interactions, and rotational diffusion. Biochemistry 34 (1995) 3893. 

Rotational relaxation times measured for several membrane proteins, mostly by the triplet phosphorescence method, are given in Table 1.5. Clearly some integral proteins rotate rather rapidly in membranes. The rotational relaxation time is defined by = 1/D where D is the rotational diffusion coefficient referred to... 

The fluid-mosaic model for biological membranes as envisioned by Singer and Nicolson. Integral membrane proteins are embedded in the lipid bilayer peripheral proteins are attached more loosely to protruding regions of the integral proteins. The proteins are free to diffuse laterally or to rotate about an axis perpendicular to the plane of the membrane. For further information, see S. J. Singer and G. L. Nicolson, The fluid mosaic model of the structure of cell membranes, Science 175 720, 1972. 

Integral proteins are usually free to move in the plane of the bilayer by lateral and rotational movement, but are not able to flip from one side of the membrane to the other (transverse movement). Immunofluorescence microscopy may be used to follow the movement of two proteins from different cells following fusion of the cells to form a hybrid heterokaryon. Immediately after fusion the two integral proteins are found segregated at either end of the heterokaryon but with time diffuse to all areas of the cell surface. The distribution of integral proteins within the membrane can be studied by electron microscopy using the freeze-fracture technique in which membranes are fractured along the interface between the inner and outer leaflets. 

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