Translational mobility of glycophorin in bilayer membranes of dimyristoylphosphatidylcholine

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Abstract
The translational diffusion of the integral membrane sialoglycoprotein from human erythrocyte membranes, glycophorin, incorporated into bilayer membranes of dimyristoylphosphatidylcholine 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 .apprx. 15.degree. C. This sharp diffusion transition is at a temperature some 9.degree. C < 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 to a localized fluidizing effect of the protein upon the gel phase lipid. The value of the diffusion coefficient > 15.degree. C was (1-2) .times. 10-8 cm2 s-1; and < 15.degree. C, it was lower than .apprx. 5 .times. 10-11 cm2 s-1. The fluorescence recovery in the bleached areas as a consequence of diffusional redistribution appeared to be due to a single diffusing species at temperatures > 15.degree. C and due to more than one diffusing species below this temperature.