CONTROL OF BAND-3 LATERAL AND ROTATIONAL MOBILITY BY BAND-4.2 IN INTACT ERYTHROCYTES - RELEASE OF BAND-3 OLIGOMERS FROM LOW-AFFINITY BINDING-SITES

Band 4.2 is a human erythrocyte membrane protein of incompletely chara cterized structure and function. Erythrocytes deficient in band 4.2 pr otein were used to examine the functional role of band 4.2 in intact e rythrocyte membranes. Both the lateral and the rotational mobilities o f band 3 were increased in band 4.2-deficient erythrocytes compared to control cells. In contrast, the lateral mobility of neither glycophor ins nor a fluorescent phospholipid analog was altered in band 4.2-defi cient cells. Compared to controls, band 4.2-deficient erythrocytes man ifested a decreased ratio of band 3 to spectrin, and band 4.2-deficien t membrane skeletons had decreased extractability of band 3 under low- salt conditions. Normal band 4.2 was found to bind to spectrin in solu tion and to promote the binding of spectrin to ankyrin-stripped inside -out vesicles. We conclude that band 4.2 provides low-affinity binding sites for both band 3 oligomers and spectrin dimers on the human eryt hrocyte membrane. Band 4.2 may serve as an accessory linking protein b etween the membrane skeleton and the overlying lipid bilayer.