Open AccessSolvent Isotope Effects on the Reaction Catalyzed by Yeast Hexokinase
Author(s) -
TAYLOR Kenneth B.,
COOK Paul F.,
CLELAND W. Wallace
Publication year - 1983
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1983.tb07604.x
Subject(s) - kinetic isotope effect , hexokinase , chemistry , deuterium , solvent , catalysis , substrate (aquarium) , yeast , isotope , inorganic chemistry , enzyme , organic chemistry , biochemistry , glycolysis , physics , biology , ecology , quantum mechanics
The pH dependence of the maximum velocity ( V ) for the phosphorylation of glucose, the V/K glucose and the V/K MgATP have been obtained in H 2 O and 2 H 2 O. In H 2 O, V decreases below a p K of 5.8, V/K glucose decreases below a p K of 6.1 and V/K MgATP decreases below a p K of 6.7. In 2 H 2 O, complex behavior is observed for these parameters as a function of pD. The ratios of the parameters in H 2 O and 2 H 2 O above their respective p K 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/K 1,5‐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 · glucose complex.