PHOSPHOTYROSINE PHOSPHATASE ASSOCIATED WITH BAND-3 PROTEIN IN THE HUMAN ERYTHROCYTE-MEMBRANE

The anion-exchange band 3 protein is the main erythrocyte protein that is phosphorylated by tyrosine kinase. To study the regulation of band 3 phosphorylation, we examined phosphotyrosine phosphatase (PTP) acti vity in the human erythrocyte. We show that the human erythrocyte memb rane contains a band 3-associated neutral PTP which is activated by Mg 2+ and inhibited by Mn2+ and vanadate. The PTP is active in the intact cell and in the isolated membrane. A major fraction of the PTP is tig htly bound to the membrane and can be extracted from it by Triton X-10 0; a minor part is associated with the Triton X-100-insoluble cytoskel eton. The behaviour of the PTP parallels that of band 3, the major fra ction of which is extractable by detergents with a minor fraction bein g anchored to the cytoskeleton. Moreover, band 3 is co-precipitated wh en the PTP is immunoprecipitated from solubilized membranes, and PTP i s co-precipitated when band 3 is immunoprecipitated. The PTP appears t o be related to PTP1B (identified using an antibody to an epitope in i ts catalytic domain and by molecular mass). The system described here has a unique advantage for PTP research, since it allows the study of the interaction of a PTP with an endogenous physiological substrate th at is present in substantial amounts in the cell membrane. The membran e-bound, band 3-associated, PTP may play a role in band 3 function in the erythrocyte and in other cells which have proteins analogous to ba nd 3.