Effect of intracellular pH changes on the distribution of tyrosine- and serine/threonine-protein kinase activities in human erythrocytes

The pH-dependence of the distribution of Tyr- and Ser/Thr-protein kinases between cytosol and membrane in human erythrocytes was investigated. When the internal pH of human erythrocytes is decreased from 8 to 7.3 the membrane-associated Tyr-protein kinase activity markedly increases at expense of the cytosolic counterpart, whereas the membrane-bound and cytosolic casein kinase activity are unaffected. This different response of the two kinase activities to the imposed variation of intracellular pH may explain why the Tyr-phosphorylation of cytoplasmic domain of band 3 results to be much higher in the ghosts from erythrocytes whose internal pH was 7.3 than that in the ghosts from erythrocytes whose internal pH was 8. By contrast, the Ser-phosphorylation of spectrin beta-subunit (band 2) and band 3 results to be practically unchanged in the ghosts from the erythrocytes treated at both pH values.