Phosphorylation of human erythrocyte band 3 by endogenous p72syk

The anion transporter, band 3, is the major tyrosine kinase substrate in both red cell membranes and intact human erythrocytes. Using antibodies to various protein-tyrosine kinases, we found that p72syk and p56/53lyn are present in human red cells, while p56lck, pp60src, p59fyn, and p55blk are absent. Treatment of intact red cells with a combination of vanadate and hydrogen peroxide dramatically increased the tyrosine phosphorylation of band 3. This treatment increased the tyrosine kinase activity of p72syk and decreased the activity of p56/53lyn in immune complex kinase assays. Band 3 was found to be associated in immune complexes with p72syk but not with p56/53lyn. These findings suggest that p72syk is responsible, at least in part, for the tyrosine phosphorylation of band 3 in human erythrocytes.