Multiple phosphorylation sites of rat liver glycogen synthase

Yuhuan Wang, Marcella Camici, Fook Thean Lee, Zafeer Ahmad, Anna A. DePaoli-Roach, Peter J. Roach

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

Rat liver glycogen synthase was purified to homogeneity by an improved procedure that yielded enzyme almost exclusively as a polypeptide of Mr 85 000. The phosphorylation of this enzyme by eight protein kinases was analyzed by cleavage of the enzyme subunit followed by mapping of the phosphopeptides using polyacrylamide gel electrophoresis in the presence of SDS, reverse-phase high-performance liquid chromatography and thin-layer electrophoresis. Cyclic AMP-dependent protein kinase, phosphorylase kinase, protein kinase C and the calmodulin-dependent protein kinase all phosphorylated the same small peptide (approx. 20 amino acids) located in a 14 kDa CNBr-fragment (CB-1). Calmodulin-dependent protein kinase and protein kinase C also modified second sites in CB-1. A larger CNBr-fragment (CB-2) of approx. 28 kDa was the dominant site of action for casein kinases I and II, FA GSK-3 and the heparin-activated protein kinase. The sites modified were all localized in a 14 kDa species generated by trypsin digestion. Further proteolysis with V8 proteinase indicated that FA GSK-3 and the heparin-activated enzyme recognized the same smaller peptide within CB-2, which may also be phosphorylated by casein kinase 1. Casein kinase 1 also modified a distinct peptide, as did casein kinase II. The results lead us to suggest homology to the muscle enzyme with regard to CB-1 phosphorylation and the region recognized by FA GSK-3, which in rabbit muscle is characterized by a high density of proline and serine residues. A striking difference with the muscle isozyme is the apparent lack of phosphorylations corresponding to the muscle sites 1a and 1b. These results provide further evidence for the presence of liver- and muscle-specific glycogen synthase isozymes in the rat. That the isozymes differ subtly as to phosphorylation sites may provide a clue to the functional differences between the isozymes.

Original languageEnglish (US)
Pages (from-to)225-236
Number of pages12
JournalBBA - Molecular Cell Research
Volume888
Issue number2
DOIs
StatePublished - Sep 19 1986

Keywords

  • (Rat Liver)
  • Glycogen synthase
  • Phosphorylation
  • Protein kinase

ASJC Scopus subject areas

  • Biophysics
  • Cell Biology
  • Molecular Biology

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