Phosphorylation of glycogen synthase by the Ca2+- and phospholipid-activated protein kinase (protein kinase C)

Z. Ahmad, F. T. Lee, Anna De Paoli-Roach, Peter Roach

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Abstract

The Ca2+- and phospholipid-dependent protein kinase (protein kinase C) has been found to phosphorylate and inactivate glycogen synthase. With muscle glycogen synthase as a substrate, the reaction was stimulated by Ca2+ and by phosphatidylserine. The tumor-promoting phorbol esters 12-O-tetradecanoyl phorbol 13-acetate was also a positive effector, half-maximal activation occurring at 6 nM. Phosphorylation of glycogen synthase, but not histone, was partially inhibited by glycogen, half-maximally at 0.05 mg/ml, probably via a substrate-directed mechanism. The rate of glycogen synthase phosphorylation was approximately half that for histone; the apparent K(m) for glycogen synthase was 0.25 mg/ml. Protein kinase C also phosphorylated casein, the preferred substrate among the individual caseins being α(s1)-casein. Glycogen synthase was phosphorylated to greater than 1 phosphate/subunit with an accompanying reduction in the -glucose-6-P/+glucose-6-P activity ratio from 0.9 to 0.5. Phosphate was introduced into serine residues in both the NH2-terminal and COOH-terminal CNBr fragments of the enzyme subunit. The two main tryptic phosphopeptides mapped in correspondence with the peptides that contain site 1a and site 2. Lesser phosphorylation in an unidentified peptide was also observed. Rabbit liver and muscle glycogen synthases were phosphorylated at similar rates by protein kinase C. The above results are compatible with a role for protein kinase C in the regulation of glycogen synthase as was suggested by a recent study of intact hepatocytes (Roach, P.J., and Goldman, M. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 7170-7172).

Original languageEnglish
Pages (from-to)8743-8747
Number of pages5
JournalJournal of Biological Chemistry
Volume259
Issue number14
StatePublished - 1984

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Glycogen Synthase
Phosphorylation
Protein Kinases
Protein Kinase C
Phospholipids
Caseins
Histones
Muscle
Substrates
Phosphates
Glucose
Phosphopeptides
Muscles
Peptides
Liver Glycogen
Phosphatidylserines
Phorbol Esters
Tetradecanoylphorbol Acetate
Glycogen
Liver

ASJC Scopus subject areas

  • Biochemistry

Cite this

Phosphorylation of glycogen synthase by the Ca2+- and phospholipid-activated protein kinase (protein kinase C). / Ahmad, Z.; Lee, F. T.; De Paoli-Roach, Anna; Roach, Peter.

In: Journal of Biological Chemistry, Vol. 259, No. 14, 1984, p. 8743-8747.

Research output: Contribution to journalArticle

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