Further purification and characterization of casein kinases from human erythrocyte hemolysate. Effect of Triton X-100

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.

Metabolic depletion effect on serine/threonine- and tyrosine-phosphorylations of membrane proteins in human erythrocytes

The response of serine/threonine-phosphorylation of the major transmembrane protein (band 3) in human erythrocytes to the metabolic state of the cells is different from that exhibited by the tyrosine-phosphorylation of the same protein. Precisely, both serine- and tyrosine-phosphorylation are decreased during metabolic depletion of the erythrocytes. However, the depletion-induced tyrosine-phosphorylation decrease of band 3 is not reversed by the subsequent metabolic repletion of the depleted cells, being accompanied by an irreversible inactivation of both membrane-bound and cytosolic tyrosine-protein kinase(s). By contrast, the depletion-induced phosphoserine-dephosphorylation is reversed by the following repletion, being accompanied by a reversible translocation of casein kinase(s) between cytosolic and membrane compartments. A possible functional correlation between the serine-phosphorylation state of band 3 protein and the band 3-mediated anion transport across the membrane is discussed.

Partial purification and characterization of cytosolic Tyr-protein kinase(s) from human erythrocytes

Tyrosine-protein kinase, phosphorylating tyrosine residues of transmembrane band 3 protein, has been partially purified from human erythrocyte cytosol by DEAE-Sepharose chromatography followed by heparin-Sepharose chromatography. Such a Tyr-protein kinase (36 kDa), as distinct from the Ser/Thre-protein kinases (casein kinase S and TS), appears to display a broader site specificity than does the previously described human erythrocyte P-Tyr-protein phosphatase, dephosphorylating band 3 protein. That is, it is able to phosphorylate not only the highly acidic copolymer poly(Glu-Tyr) but also angiotensin II, lacking an acidic amino acid sequence around the target Tyr residue. Moreover, the phosphorylation of these two substrates exhibits a different pH dependence and a different response to NaCl and 2,3-bisphosphoglycerate. These results suggest that in intact erythrocytes the cytosolic Tyr-protein kinase might phosphorylate band 3 not only on Tyr-8, surrounded by several acidic side-chains (as demonstrated preferentially to occur in isolated ghosts), but also on other Tyr residues surrounded by other amino acid sequences.