Rotational diffusion of band 3 proteins in membranes from En(a—) and neuraminidase-treated normal human erythrocytes

Abstract

Recent experiments have demonstrated an association between band 3 and glycophorin A in the human erythrocyte membrane (Nigg, E.A., Bron, C., Girardet, M. and Cherry, R.J. (1980) Biochemistry 19, 1887–1893). Here, the influence of sialoglycoproteins on the rotational diffusion of band 3 in the human erythrocyte membrane was investigated by studying membranes from En(a—) and neuraminidase-treated erythrocytes. Rotational diffusion was measured by observing flash-induced transient dichroism of eosin-labeled band 3. Although erythrocytes of the rare phenotype En(a—) lack the major sialoglycoprotein, glycophorin A, no significant difference in band 3 rotation at pH 7.4 and 37°C could be detected between En(a—) and normal erythrocyte membranes. Band 3 rotation at pH 7.4 was also insensitive to the enzymatic removal of sialic acid from the surface of normal erythrocytes. Moreover, the existence of an essentially similar temperature-dependent equilibrium between band 3 proteins with different mobilities was observed in normal, En(a—) and neuraminidase-treated erythrocytes. From these results it is concluded that glycophorin A contributes less than 15% to the cross-sectional diameter of the band 3-glycophorin A complex in the plane of the normal membrane. The rotation of the complex at pH 7.4 is not significantly influenced by either steric or electrostatic interactions involving the oligosaccharide moiety of glycophorin A.