Sensitivity of the Essential Zinc-Thiolate Moiety of Yeast Alcohol Dehydrogenase to Hypochlorite and Peroxynitrite

Disruption of the zinc-thiolate center at the active site of yeast alcohol dehydrogenase results in inactivation and zinc release. Measurements of activity, zinc release, and thiol/thiolate oxidation were used to assess the effects of biologically relevant oxidants on alcohol dehydrogenase. Alcohol dehydrogenase was inactivated by 1 mM hydrogen peroxide at a rate of 1.3 M-1 s-1. Peroxynitrite, the near diffusion-limited reaction product of nitric oxide and superoxide, inactivated alcohol dehydrogenase with an IC50 = 0.95 microM when catalytic concentrations of alcohol dehydrogenase subunit (0.074 microM) were present. Slow, continuous production of peroxynitrite from decomposition of SIN-1 inactivated alcohol dehydrogenase as effectively as bolus addition. The rate constants for reaction of peroxynitrite with alcohol dehydrogenase at 23 degrees C as determined by two different competition assays were 2.6 x 10(5) M-1 s-1 and 5.2 x 10(5) M-1 s-1. The reaction with alcohol dehydrogenase represents one of the fastest reactions yet determined for peroxynitrite. Hypochlorite inactivated alcohol dehydrogenase at a rate of 4 x 10(3) M-1 s-1. The rate constant for inactivation by taurine choramine, the reaction product of taurine and hypochlorite, was only slightly slower at 2.7 x 10(3) M-1 s-1. Zinc release and thiol/thiolate oxidation were correlated with inactivation by either peroxynitrite or hypochlorite. At the concentrations of peroxynitrite or hypochlorite producing total inactivation, 0.85 zinc atom was released per subunit and 3 thiol/thiolates per subunit were oxidized.(ABSTRACT TRUNCATED AT 250 WORDS)