L Waxman

The phosphorylation of the major proteins of the human erythrocyte membrane.

Abstract Both the major sialoglycoprotein (PAS-1) and the component designated by Fairbanks et al. ( G. Fairbanks, T. L. Steck, and D. F. H. Wallach, 1971 , Biochemistry 10 , 2606–2617) as Band 3 are shown to be bonafide phosphoproteins by virtue of the presence of covalently bound serine and threonine phosphate residues. In agreement with the findings of others, PAS-1 does not seem to be phosphorylated when ghosts are incubated with [γ- 32 P]ATP, but the phosphorylation is significant (about 0.15 mol/mol) when the cells are incubated in the presence of 32 P i . Band 3 is phosphorylated to the extent of 0.90 mol/mol, and these sites are apparently distributed in several places along the polypeptide chain. Spectrin is also a phosphoprotein containing approximately four molecules of phosphate per 450,000 daltons of protein. The phosphorylation of these three polypeptides is not stimulated by the presence of cAMP.