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

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Abstract
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)4:1 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.