Mechanism of action of heavy metals, S-triazine herbicides and nitrates on alcohol dehydrogenase from rape

Abstract

Heavy metals (Pb2+, Cu2+, Cd2+, and Zn2+) inhibited alcohol dehydrogenase (ADH) of rape (EC 1.1.1.1.); Pb2+ and Cd2+ ions affected the imidazole ring of histidine, Cu2+ and Zn2+ ions interacted with the sulphydryl groups of cysteine in the molecule of the enzyme. The coenzyme protected ADH from inactivation by Pb2+ and Cd2+, but did not protect it from Cu2+ and Zn2+. Ethanol in a ternary complex ADH-NAD+ -ethanol was a strong protecting agent from Pb2+ and Cd2+ ions. Nitrates inhibited rape ADH toward any substrate. Sulphates and fluorides had no effect. The S-triazine herbicides studied proved strong inhibitors of rape ADH (their Ki's corresponded to concentrations of the order 10-4 mol 1-1), occupying the binding site for the coenzyme. The herbicides interacted with the metallic component of the enzyme, to which the nicotinamide part of the coenzyme is bound.