The Peroxidatic Reaction Catalyzed by Horse Liver Alcohol Dehydrogenase

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Abstract
The results of steady-state kinetic measurements on the initial rate of the peroxidatic reaction between .beta.-NAD+ and H2O2, catalyzed by horse liver alcohol dehydrogenase, at pH 7 are described. A simple sequential mechanism is deduced from graphical analysis of the data plotted according to Eadie-Augustinsson-Hofstee primary plots and the values of the true kinetic parameters .**GRAPHIC**. .**GRAPHIC**. and Vmax are estimated from the corresponding secondary plots. Ethanol compete H2O2, for the same enzyme active site. During the catalytic process a progressive inactivation of the enzyme occurs, caused by H2O2. The rate law of this process is quantitatively described at pH 7 in the absence and presence of NAD+. The coenzyme protected the enzyme against inactivation by H2O2, which oxidized essential cysteine residues. The results obtained from the study of catalytic and inactivating processes are rationalized on the basis of a general mechanistic scheme.

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