Effect of heterocyclic compounds and 2-mercaptoethanol on rape alcohol dehydrogenase

Rape alcohol dehydrogenase (ADH) is inhibited by heterocyclic compounds with a five- to six-membered ring (imidazole, pyrazole, 4-methylpyrazole, 3-methylpyrazole, pyridine, nicotine amide) and by o-phenanthroline, a heterocyclic, polycyclic compound. Pyrazole and its derivatives, imidazole and pyridine, are competitive inhibitors with respect to ethanol. Nicotine amide and o-phenanthroline behave as mixed inhibitors (competitive – noncompetitive) with respect to the substrate. The addition of Zn2+-ions to the reaction medium interferes with the competition by o-phenanthroline. 4-Methylpyrazole and pyrazole are the strongest inhibitors of rape ADH. 2-Mercaptoethanol is an inhibitor of rape ADH which competes with ethanol and the coenzyme. The reversible inhibition by mercaptoethanol changes into the irreversible inactivation of the enzyme. The binding of inhibitors to the zinc atom present in the molecule of rape ADH and the localization of the metal in the enzyme protein have been studied.