Journal of the Chemical Society. Perkin transactions II p. 2071 - 2076 (1988)
Update date:2022-08-05
Topics:
Carrington, Simon J.
Douglas, Kenneth T.
Glyoxalase I (EC 4.4.1.5), purified to homogeneity from human erythrocytes, catalyses the rearrangement to α-hydroxymandeloylglutathiones of the hemithioacetals formed by equilibration of glutathione with para-substituted arylglyoxals.The association constants describing these equilibria were measured at 25 degC, pH 7.0.Values of kcat, Km and kcat/Km, describing the substrate behaviour of these hemithioacetals towards human erythrocyte glyoxalase I, were determined at pH 7.0 and 25 degC.Hammett analysis showed a linear correlation only for kcat(ρ+0.43)versus Hammett ? constants.Literature data for glyoxalase I from yeast showed similar behaviour (ρ+0.47).In both cases good correlation required exclusion of the unsubstituted phenylglyoxal data and consideration only of para-substituted substrates.A linear free energy relationship was found between kcat values for the human erythrocyte glyoxalase I-catasysed reaction and the rearrangement step for the model, non-enzymatic reaction.Comparisons of model and enzymatic cases on the basis of Hammett sensitivities and primary deuterium isotope effects indicated that both model and enzymatic transition states are probably closely similar and involve rate-determining deprotonation of the C-H bond adjacent to the sulphur atom in the hemithioacetal.
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