Phosphorylation of human erythrocyte band 3 by endogenous p72^syk

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 p72^syk and p56/53^lyn are present in human red cells, while p56^lck, pp60^src, P59^fyn and p55^blk 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 p72^syk and decreased the activity of P56/53^lyn in immune complex kinase assays. Band 3 was found to be associated in immune complexes with p72^syk but not with p56/53^lyn. These findings suggest that p72^syk is responsible, at least in part, for the tyrosine phosphorylation of band 3 in human erythrocytes.