Phorbol ester stimulates the phosphorylation of rabbit erythrocyte band 4.1

The effect of phorbol esters on membrane phosphorylation was examined in intact rabbit erythrocytes prelabeled with [32P]orthophosphate. Tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate, but not the inactive 4 alpha-phorbol 12,13-didecanoate, specifically stimulated the phosphorylation of two proteins in the erythrocyte membrane. They have apparent molecular weight of 100,000 dalton and 85,000 dalton. When intracellular calcium concentrations were raised by ionomycin, A23187, both the 85,000 dalton polypeptide and the 85K phosphoprotein were degraded. The 85,000 dalton phosphoprotein showed cross-reactivity with antiserum to human erythrocyte band 4.1. Based on its susceptibility to calcium-activated protease and its immunological property, the 85,000 dalton phosphoprotein was identified to be the band 4.1 of the erythrocyte membrane skeletal network.