title: Threonine phosphorylation of rat liver glycogen synthase.
abstract: 32P-labeled glycogen synthase specifically immunoprecipitated from 32P-phosphate incubated rat hepatocytes contains, in addition to [32P] phosphoserine, significant levels of [32P] phosphothreonine (7% of the total [32P] phosphoaminoacids). When the 32P-immunoprecipitate was cleaved with CNBr, the [32P] phosphothreonine was recovered in the large CNBr fragment (CB-2, Mapp 28 Kd). Homogeneous rat liver glycogen synthase was phosphorylated by all the protein kinases able to phosphorylate CB-2 "in vitro" (casein kinases I and II, cAMP-dependent protein kinase and glycogen synthase kinase-3). After analysis of the immunoprecipitated enzyme for phosphoaminoacids, it was observed that only casein kinase II was able to phosphorylate on threonine and 32P-phosphate was only found in CB-2. These results demonstrate that rat liver glycogen synthase is phosphorylated at threonine site(s) contained in CB-2 and strongly indicate that casein kinase II may play a role in the "in vivo" phosphorylation of liver glycogen synthase. This is the first protein kinase reported to phosphorylate threonine residues in liver glycogen synthase.
authors.forename: J
authors.initials: J
authors.lastname: Ariño
authors.forename: M
authors.initials: M
authors.lastname: Arró
authors.forename: J J
authors.initials: JJ
authors.lastname: Guinovart
mesh_terms: D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D047388:Casein Kinases; D006006:Glycogen Synthase / Q000302:isolation & purification / Q000378:metabolism*; D038341:Glycogen Synthase Kinases; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology*; D008297:Male; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D010769:Phosphothreonine / Q000302:isolation & purification*; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013912:Threonine / Q000031:analogs & derivatives*
chemical_list: D010761:Phosphorus Radioisotopes; D010769:Phosphothreonine; D013912:Threonine; D006006:Glycogen Synthase; D011494:Protein Kinases; D038341:Glycogen Synthase Kinases; D047388:Casein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases