title: Apparent activation of the MgATP-dependent protein phosphatase by pp60v-src. Identification of an activity like that of glycogen synthase kinase 3 in immunoaffinity purified pp60v-src preparations.
abstract: Immunoaffinity purified pp60v-src was found to activate the MgATP-dependent protein phosphatase in the presence of MgATP. Although preliminary evidence suggested that phosphorylation of the inhibitor-2 subunit on tyrosine residues was responsible for the activation, preincubation of the pp60v-src preparation at 41 degrees C resulted in a rapid loss of its protein kinase activities towards both casein and inhibitor-2 while its ability to activate the protein phosphatase complex was relatively insensitive to this treatment. This result demonstrated that pp60v-src was not responsible for activation of the MgATP-dependent protein phosphatase. A protein kinase activity which phosphorylated glycogen synthase on serine residues was detected in the pp60v-src preparation. The protein kinase was active in the presence of inhibitors of phosphorylase kinase, glycogen synthase kinase 5/casein kinase II, and cAMP-dependent protein kinase. It is, therefore, likely that activation of the MgATP-dependent protein phosphatase resulted from the presence of a glycogen synthase kinase 3 like activity in the pp60v-src preparation. Our results illustrate the importance of applying multiple criteria to link the phosphorylation of a protein with an observed change in its activity.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002846:Chromatography, Affinity; D004789:Enzyme Activation; D038341:Glycogen Synthase Kinases; D006358:Hot Temperature; D066298:In Vitro Techniques; D015688:Oncogene Protein pp60(v-src); D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011817:Rabbits; D012191:Retroviridae Proteins / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D012191:Retroviridae Proteins; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D015688:Oncogene Protein pp60(v-src); D038341:Glycogen Synthase Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases