Phosphorylation of membrane proteins by cytosolic casein kinases in human erythrocytes. Effect of monovalent ions, 2,3-bisphosphoglycerate and spermine

Summary

Membrane proteins of human erythrocytes can be phosphorylated not only by membrane casein kinase (MS) but also by cytosolic casein kinases CS and CTS, resembling casein kinase I and II, respectively.

Casein kinase CS, like membrane casein kinase MS, preferentially phosphorylates membrane proteins such as band 2 (spectrin, β-subunit) and band 3, which are the major phosphate-acceptor proteins in the endogenous phosphorylation of isolated ghosts in the presence of [γ-³²P]ATP.

By contrast, cytosolic casein kinase CTS phosphorylates, in addition to band 2, some membrane proteins, whose endogenous phosphorylation in isolated ghosts under the same conditions is negligible, if any.

The CS- and CTS-catalyzed phosphorylations exhibit different response to increasing NaCl (or KCI) concentrations up to physiological levels (140 mM KCI, 20 mM NaCI); i.e. CS-and MS-catalyzed phosphorylations are strongly inhibited by 75–150 mM KCI (or NaCl), while CTS-catalyzed phosphorylation is practically unaffected.

In the absence of added NaCl, CS- and MS-catalyzed phosphorylations are markedly inhibited by 1.5-3 mM 2,3-bisphosphoglycerate, whereas CTS-catalyzed phosphorylation appears to be practically unaffected.

Finally, CS- and MS-catalyzed phosphorylations are slightly inhibited also by 1 mM spermine, while CTS-catalyzed phosphorylation is enhanced by this polycation concentration.