title: Some aspects of the phosphorylation of phenylalanine 4-monooxygenase by a calcium-dependent and calmodulin-dependent protein kinase.
abstract: A calmodulin-dependent protein kinase purified from liver catalyzed the incorporation of up to 0.7 mol of phosphate per mol subunit of phenylalanine 4-monooxygenase. The phosphorylation was accompanied by a proportional increase in the hydroxylase activity. The reaction was Ca2+-dependent and was inhibited by physiological concentrations of phenylalanine. Phenylalanine 4-monooxygenase was also a substrate for the cGMP-dependent protein kinase, but in this system phenylalanine stimulated the rate of phosphorylation to a similar extent as that observed in the reaction catalyzed by cAMP-dependent protein kinase. The hydroxylase was not a substrate for phosphorylase kinase. The calmodulin-dependent reversal of the kinase reaction in the presence of MgADP, was also inhibited by phenylalanine. Since the kinetics of the reverse reaction was the same using 32P-hydroxylase phosphorylated by calmodulin-dependent and cAMP-dependent kinases, it is likely that both kinases phosphorylate the same site on the enzyme. This conclusion was further supported by peptide mapping of tryptic and peptic digests of 32P-hydroxylase, which revealed one major phosphopeptide with enzyme phosphorylated by either kinase. The Ca2+-dependent and calmodulin-dependent phosphorylation described above may mediate the increased phosphorylation of the hydroxylase [Garrison, J. C., Johnsen, D. E., and Campanile, C. P. (1984) J. Biol. Chem. 259, 3283-3292] and its increased activity [Fisher, M. J., Santana, M. A., and Pogson, C. I. (1984) Biochem. J. 219, 87-90] recently observed in hepatocytes exposed to Ca2+-elevating agents.
mesh_terms: D000818:Animals; D001345:Autoradiography; D002118:Calcium / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D008099:Liver / Q000201:enzymology; D009712:Nucleotides, Cyclic / Q000502:physiology; D010649:Phenylalanine / Q000494:pharmacology; D010651:Phenylalanine Hydroxylase / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats
chemical_list: D002147:Calmodulin; D009712:Nucleotides, Cyclic; D010649:Phenylalanine; D010651:Phenylalanine Hydroxylase; D011494:Protein Kinases; D002118:Calcium