1. The kinetics of oxidation of ethanol, propan-1-ol, butan-1-ol and propan-2-ol by NAD+ and of reduction of acetaldehyde and butyraldehyde by NADH catalysed by yeast alcohol dehydrogenase were studied. 2. Results for the aldehyde–NADH reactions are consistent with a compulsory-order mechanism with the rate-limiting step being the dissociation of the product enzyme–NAD+ complex. In contrast the results for the alcohol–NAD+ reactions indicate that some dissociation of coenzyme from the active enzyme–NAD+–alcohol ternary complexes must occur and that the mechanism is not strictly compulsory-order. The rate-limiting step in ethanol oxidation is the dissociation of the product enzyme–NADH complex but with the other alcohols it is probably the catalytic interconversion of ternary complexes. 3. The rate constants describing the combination of NAD+ and NADH with the enzyme and the dissociations of these coenzymes from binary complexes with the enzyme were measured.

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