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

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, beta-subunit) and band 3, which are the major phosphate-acceptor proteins in the endogenous phosphorylation of isolated ghosts in the presence of [gamma-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 KCl) concentrations up to physiological levels (140 mM KCl, 20 mM NaCl); i.e. CS- and MS-catalyzed phosphorylations are strongly inhibited by 75-150 mM KCl (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.