Glycogen synthase kinases. Classification of a rabbit liver casein and glycogen synthase kinase (casein kinase-1) as a distinct enzyme

Z. Ahmad, M. Camici, A. A. DePaoli-Roach, P. J. Roach

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A protein kinase, able to phosphorylate casein, phosvitin, and glycogen synthase, was purified approximately 9000-fold from rabbit liver, and appeared analogous to an enzyme studied by Itarte and Huang (Itarte, E., and Huang, K.-P. (1 979) J. Biol. Chem. 254, 4052-4057). This enzyme, designated here casein kinase-1, was shown to be a distinct glycogen synthase kinase and in particular to be different from the protein kinase GSK-3 (Hemmings, B.A., Yellowlees, D., Kernohan, J.C., and Cohen, P. (1981) Eur. J. Biochem. 119, 443-451). Casein kinase-1 had native molecular weight of 30,000 as judged by gel filtration. The enzyme phosphorylated β-casein A or B better than κ-Casein or α(s1)-casein, and modified only serine residues in β-casein B and phosvitin. The apparent K(m) for ATP was 11 μM, and GTP was ineffective as a phosphoryl donor. The phosphorylation of glycogen synthase by casein kinase-1 was inhibited by glycogen, half-maximally at 2 mg/ml, and by heparin, half-maximally at 0.5-1.0 μg/ml, but was unaffected by Ca2+ and/or calmodulin, or by cyclic AMP. Phosphorylation of muscle glycogen synthase proceeded to a stoichiometry of at least 6 phosphates/subunit with reduction in the ± glucose-6-P activity ratio to less than 0.4. Phosphate was introduced in both a COOH-terminal CNBr fragment (CB-2) as well as a NH2-terminal fragment (CB-1). At a phosphorylation stoichiometry of 6 phosphates/subunit, 84% of the phosphate was associated with CB-2 and 6.5% with CB-1. The remainder of the phosphate was introduced into another CNBr fragment of apparent molecular weight 16,500. Phosphorylation by casein kinase-1 correlated with reduced electrophoretic mobilities, as analyzed on polyacrylamide gels in the presence of sodium dodecyl sulfate, of the intact glycogen synthase subunit, as well as the CNBr fragments CB-1 and CB-2.

Original languageEnglish (US)
Pages (from-to)3420-3428
Number of pages9
JournalJournal of Biological Chemistry
Issue number6
StatePublished - Jan 1 1984

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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