Inactivation of yeast alcohol dehydrogenase by nitrilopropionamides

A series of halonitrilopropionamides have been examined as potential inhibitors of yeast alcohol dehydrogenase. Analogues with a good leaving group on the alpha-carbon, and a geminal electronegative atom, were found to be initial competitive inhibitors against NAD with inhibition constants as low as 0.6 microM. Incubation of the enzyme with these inhibitors leads to a slow, irreversible inactivation, with an inactivation constant for 2,2-dibromo-3-nitropropionamide of about 100 microM. No protection against inactivation was observed with the substrate ethanol, while the presence of saturating levels of NAD slowed the rate, but not the final extent, of enzyme inactivation. The resulting enzyme-inactivator complex is stable to a range of conditions that are known to denature the enzyme, indicating that a covalent modification of yeast alcohol dehydrogenase has led to the inactivation. A bimodal inactivation model is proposed to account for the observed interactions of these halonitrilopropionamides with yeast alcohol dehydrogenase.