title: Chemical mechanism of the adenosine cyclic 3',5'-monophosphate dependent protein kinase from pH studies.
abstract: The pH dependence of kinetic parameters and inhibitor dissociation constants for the adenosine cyclic 3',5'-monophosphate dependent protein kinase reaction has been determined. Data are consistent with a mechanism in which reactants selectively bind to enzyme with the catalytic base unprotonated and an enzyme group required protonated for peptide (Leu-Arg-Arg-Ala-Ser-Leu-Gly) binding. Binding of the peptide apparently locks both of the above enzyme residues in their correct protonation state. MgATP preferentially binds fully ionized and requires an enzyme residue (probably lysine) to be protonated. The maximum velocity and V/KMgATP are pH independent. The V/K for Ser-peptide is bell-shaped with pK values of 6.2 and 8.5 estimated. The pH dependence of 1/Ki for Leu-Arg-Arg-Ala-Ala-Leu-Gly is also bell-shaped, giving pK values identical with those obtained for V/KSer-peptide, while the Ki for MgAMP-PCP increases from a constant value of 650 microM above pH 8 to a constant value of 4 mM below pH 5.5. The Ki for uncomplexed Mg2+ obtained from the Mg2+ dependence of V and V/KMgATP is apparently pH independent.
authors.affiliation: Department of Biochemistry, North Texas State University/Texas College of Osteopathic Medicine, Denton 76203.
authors.forename: M Y
authors.initials: MY
authors.lastname: Yoon
authors.forename: P F
authors.initials: PF
authors.lastname: Cook
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D000242:Cyclic AMP / Q000494:pharmacology*; D003903:Deuterium; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009842:Oligopeptides / Q000378:metabolism; D011494:Protein Kinases / Q000502:physiology*
chemical_list: D009842:Oligopeptides; C037642:kemptide; D000255:Adenosine Triphosphate; D003903:Deuterium; D000242:Cyclic AMP; D011494:Protein Kinases; D008274:Magnesium