title: Characterization of an autophosphorylation-dependent multifunctional protein kinase from liver.
abstract: A cyclic nucleotide- and Ca2+-independent protein kinase has been identified and purified from pig liver to apparent homogeneity. This independent protein kinase is basically inactive but can be activated by a 4-min incubation with 0.25 mM ATP and 2 mM Mg2+. This ATP X Mg-mediated activation appears to involve an intramolecular autophosphorylation as it is independent of kinase concentration. Phosphoamino acid analysis further indicates that this intramolecular autophosphorylation/activation process is predominantly on a serine residue. The nonphosphorylated, inactive form of the kinase is extremely trypsin-labile, whereas the phosphorylated, active kinase is more resistant to trypsin, suggesting a conformational change during the activation process. Autophosphorylation/activation of the kinase is enhanced 2-fold by heparin (0.4 unit/ml) and blocked by phosphatidylserine (0.4 mg/ml). Partial dephosphorylation of the phosphorylated kinase is associated with a time-dependent decrease in the enzyme activity. This autophosphorylation-dependent protein kinase phosphorylates glycogen synthase (Km = 8 microM) at sites 2 and 3, resulting in inactivation of glycogen synthase. The results indicate that this independent kinase may represent a previously undiscovered liver multifunctional protein kinase which can be regulated by reversible phosphorylation.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002850:Chromatography, Gel; D004789:Enzyme Activation; D006493:Heparin / Q000494:pharmacology; D008099:Liver / Q000201:enzymology*; D008274:Magnesium / Q000378:metabolism; D009132:Muscles / Q000201:enzymology; D010718:Phosphatidylserines / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D011817:Rabbits
chemical_list: D010718:Phosphatidylserines; D000255:Adenosine Triphosphate; D006493:Heparin; D011494:Protein Kinases; D008274:Magnesium