Thermodynamic profiles for alcohol dehydrogenase action in free solution

Abstract

Stopped-flow equipment was used to study the kinetics of the reaction between nicotinamide adenine dinucleotide (NAD) and ethanol, catalyzed by yeast alcohol dehydrogenase. By measuring rates over a range of concentrations of NAD and ethanol and of temperatures, thermodynamic profiles were obtained for the reaction, which occurs by an ordered ternary complex mechanism with NAD adding first. There are significant negative entropies of activation and negative entropy changes for the additions of NAD and of ethanol; the breakdown of the ternary complex is, however, accompanied by a positive entropy of activation. The results are consistent with structural constraints associated with the binding of the substrates, these restraints being to some extent removed when the ternary complex undergoes reaction. The system follows a similar pattern to that found with three different varieties of lactate dehydrogenase.