Interaction of protein 4.1 with the red cell membrane: effects of phosphorylation by protein kinase C.

Phosphorylation with endogenous protein kinase C causes the membrane skeletal protein, band 4.1, to lose its capacity to attach to one of two classes of high-affinity binding sites on the red cell membrane. These sites are the ones eliminated by proteolysis in situ of glycophorin C; the surviving type of site is located in a C-terminal peptide of the glycophorin C, retained on the membrane after proteolysis, which is also the site of attachment of p55. A synthetic peptide, comprising the 28 C-terminal residues of glycophorin C, also binds protein 4.1. Phosphorylation of the intact cells, stimulated by phorbol ester, approximately halves the retention of glycophorin C in the membrane cytoskeletons prepared from these cells and reduces the affinity of extracellular glycophorin C epitopes for their antibody.