Purification and characterization of Mg2+-dependent glycogen synthase phosphatase (phosphoprotein phosphatase IA) from rat liver

Eur J Biochem. 1981 Oct;119(3):503-10. doi: 10.1111/j.1432-1033.1981.tb05636.x.


Phosphoprotein phosphatase IA, which represents the major glycogen synthase phosphatase activity in rat liver cytosol, has been purified to apparent homogeneity by chromatography on DEAE-cellulose, histone - Sepharose-4B and Sephadex G-100. The molecular weight of the purified enzyme was 40 000 by gel filtration and 48 000 by sodium dodecyl sulfate gel electrophoresis, Phosphatase IA is therefore a monomeric protein. When treated with 80% ethanol at room temperature, phosphatase IA underwent an inactivation which was totally prevented by 2 mM MgCl2. Catalytically, phosphatase IA has a preference for glycogen synthase D compared with phosphatases IB and II and obligatorily requires Mg2+ or Mn2+ for activity. Maximum activity was attained at 5 mM MgCl2. Since Mg2+ does not activate other phosphoprotein phosphatases in rat liver cytosol, we propose the term 'Mg2+-dependent glycogen synthase phosphatase' for phosphatase IA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chromatography
  • Cytosol / enzymology
  • Enzyme Activation / drug effects
  • Glycogen-Synthase-D Phosphatase / isolation & purification*
  • Liver / enzymology*
  • Magnesium / pharmacology
  • Male
  • Phosphoprotein Phosphatases / isolation & purification*
  • Rats
  • Rats, Inbred Strains


  • Phosphoprotein Phosphatases
  • Glycogen-Synthase-D Phosphatase
  • Magnesium