title: Direct determination of creatine kinase equilibrium constants with creatine or cyclocreatine substrate.
abstract: The equilibrium constants of two reactions catalyzed by rabbit muscle creatine kinase with creatine or cyclocreatine as substrate were determined by 31P-NMR. The value of the equilibrium constant with creatine as substrate was 172.10(7) M(-1) in agreement with previous work (Veech, R.L., Lawson, J.W.R., Cornell, W. and Krebs, H.A. (1979) J. Biol. Chem 254, 6538-6547). The value with cyclocreatine was 5.62.10(7) M(-1) and the ratio of the two constants is 30.6. It was possible to determine the ratio of the two equilibrium constants in a reaction mixture containing both substrates since it was found that the 31P resonances of P-creatine and P-cyclocreatine were well resolved. The ratio of K1/K2 determined in such experiments was 34.6, of the same order as previously reported by Annesley and Walker (Annesley, T.M. and Walker, J.B. (1977) Biochem. Biophys. Res. Commun. 74, 185-190).
authors: Department of Biochemistry and Biophysics, University of PA School of Medicine, Philadelphia.
authors: P
authors: P
authors: LoPresti
authors: M
authors: M
authors: Cohn
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D003401:Creatine / Q000378:metabolism*; D003402:Creatine Kinase / Q000378:metabolism*; D003404:Creatinine / Q000031:analogs & derivatives* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy
chemical_list: D000244:Adenosine Diphosphate; C012260:cyclocreatine; D000255:Adenosine Triphosphate; D003404:Creatinine; D003402:Creatine Kinase; D003401:Creatine