Translational mobility of glycophorin in bilayer membranes of dimyristoylphosphatidylcholine.

The translational diffusion of the integral membrane sialoglycoprotein from erythrocyte membranes, glycophorin, incorporated into bilayer membranes of dimyristoyl-phosphatidylcholine at a protein/lipid molar ratio of 1:4500 was examined by using the fluorescence redistribution after photobleaching technique. A plot of the diffusion coefficient vs. temperature shows a sharp decrease in the rate of diffusion at about 15 degrees C. This sharp diffusion transition is at a temperature some 9 degrees C lower than the calorimetrically measured lipid gel-liquid crystalline phase transition temperature of the system. The difference between the diffusion transition temperature and the lipid phase transition temperature is attributed toi a localized fluidizing effect of the protein upon the gel phase lipid. The value of the diffusion coefficient above 15 degrees C was found to be (1-2) x 10(-8) cm(2)s(-1), and below 15 degrees C it was lower than about 5 x 10(-11)cm(2)s(-1). The fluorescence recovery in the bleached area as a consequence of diffusional redistribution appeared to be due to a single diffusing species at temperatures above 15 degrees C and due to more than one diffusing species below this temperature.