Alterations of glycoprotein distribution and lateral mobility in cell membranes can provide transmembrane signals for several membrane-related phenomena1-3. Control of the transmembranous events has been ascribed to interaction between submembranous protein matrices (or 'cytoskeletons') and membrane glycoproteins4-7. A consequence of such interaction would be differential inhibition of protein lateral diffusion in biological membranes. Measurements of the lateral diffusion coefficients of membrane proteins, in fact, have generally yielded values8-12 much less than were predicted for unhindered diffusion in a fluid bilayer13,14. The mouse spherocytic erythrocyte, which lacks the major components of the normal erythrocyte membrane matrix15 (composed of spectrin, actin, bands 4.1 and 4.9 (ref. 16), in the nomenclature of Fairbanks et al.17), provides a unique system for a direct evaluation of the effect of the matrix on protein lateral mobility. After using a modification of the technique of fluorescence redistribution after photobleaching (FRAP)18, we report here that membrane proteins diffuse about 50 times faster in spherocytic than in normal mouse erythrocytes.
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