title: Solvent isotope effects on the reaction catalyzed by yeast hexokinase.
abstract: The pH dependence of the maximum velocity (V) for the phosphorylation of glucose, the V/Kglucose and the V/KMgATP have been obtained in H2O and 2H2O. In H2O, V decreases below a pK of 5.8, V/Kglucose decreases below a pK of 6.1 and V/KMgATP decreases below a pK of 6.7. In 2H2O, complex behavior is observed for these parameters as a function of pD. The ratios of the parameters in H2O and 2H2O above their respective pK values give solvent deuterium isotope effects of about 1.5-1.7 for all three parameters. When 1,5-anhydromannitol is used as an alternative substrate, an isotope effect different than unity is obtained only for V/K1,5-anhydromannitol which gives a value of about 0.7. Both the complex pH profiles and the relative magnitude of the isotope effects are interpreted in terms of a pH-dependent change in the E X glucose complex.
mesh_terms: D002384:Catalysis; D003903:Deuterium; D005947:Glucose / Q000378:metabolism; D006593:Hexokinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007553:Isotope Labeling; D007700:Kinetics; D008956:Models, Chemical; D010766:Phosphorylation; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D012997:Solvents
chemical_list: D012997:Solvents; D003903:Deuterium; D006593:Hexokinase; D005947:Glucose