title: Stereochemical control over Mn(II)-thio versus Mn(II)-oxy coordination in adenosine 5'-O-(1-thiodiphosphate) complexes at the active site of creatine kinase.
abstract: The stereochemical configurations of the Mn(II) complexes with the resolved epimers of adenosine 5'-O-(1-thiodiphosphate) (ADP alpha S), bound at the active site of creatine kinase, have been determined in order to assess the relative strengths of enzymic stereoselectivity versus Lewis acid/base preferences in metal-ligand binding. Electron paramagnetic resonance (EPR) data have been obtained for Mn(II) in anion-stabilized, dead-end (transition-state analogue) complexes, in ternary enzyme-MnIIADP alpha S complexes, and in the central complexes of the equilibrium mixture. The modes of coordination of Mn(II) at P alpha in the nitrate-stabilized, dead-end complexes with each epimer of ADP alpha S were ascertained by EPR measurements with (Rp)-[alpha-17O]ADP alpha S and (Sp)-[alpha-17O]ADP alpha S. The EPR spectrum for the complex with (Rp)-[alpha-17O]ADP alpha S showed inhomogeneous broadening due to unresolved superhyperfine coupling from coordinated 17O at P alpha. By contrast, the EPR spectrum for Mn(II) in complex with (Sp)-[alpha-17O]ADP alpha S is indistinguishable from that obtained for a matched sample with unlabeled (Sp)-ADP alpha S. A reduction in the magnitude of the 55Mn hyperfine coupling constant in the spectrum for the complex containing (Sp)-ADP alpha S is indicative of Mn(II)-thio coordination at P alpha.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Institute for Enzyme Research, Graduate School, University of Wisconsin, Madison 53705.
authors.forename: G W
authors.initials: GW
authors.lastname: Smithers
authors.forename: R D
authors.initials: RD
authors.lastname: Sammons
authors.forename: P J
authors.initials: PJ
authors.lastname: Goodhart
authors.forename: R
authors.initials: R
authors.lastname: LoBrutto
authors.forename: G H
authors.initials: GH
authors.lastname: Reed
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D003402:Creatine Kinase / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism*; D008968:Molecular Conformation; D009132:Muscles / Q000201:enzymology; D011817:Rabbits; D013379:Substrate Specificity; D013873:Thionucleotides / Q000378:metabolism*
chemical_list: D013873:Thionucleotides; D008345:Manganese; C018444:adenosine 5'-O-(1-thiodiphosphate); D000244:Adenosine Diphosphate; D003402:Creatine Kinase; D008274:Magnesium