title: Purification and characterization of Mg2+-dependent glycogen synthase phosphatase (phosphoprotein phosphatase IA) from rat liver.
abstract: 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.
mesh_terms: D000818:Animals; D002845:Chromatography; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D006007:Glycogen-Synthase-D Phosphatase / Q000302:isolation & purification*; D008099:Liver / Q000201:enzymology*; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D010749:Phosphoprotein Phosphatases / Q000302:isolation & purification*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D010749:Phosphoprotein Phosphatases; D006007:Glycogen-Synthase-D Phosphatase; D008274:Magnesium