A comparative study of the effect of triazine herbicides on alcohol dehydrogenases isolated from various sources.

The studied herbicides (terbutylazine, simazine) inhibit the activity of plant, animal, and yeast alcohol dehydrogenases. The inhibition constant Ki for alcohol dehydrogenase (ADH) isolated from peas and bakers' yeast equals approximately 10(-4) M, and that for ADH isolated from horse liver is of the order of 10(-5) M. The character of inhibition for all the herbicides studied for the reaction catalyzed by pea, liver, and yeast ADH is always noncompetitive toward ethanol and competitive with respect to NAD. The inhibition constants for the enzyme isolated from peas are pH independent. The interaction constants found for terbutylazine and simazine and for o-phenanthroline, nicotinamide, and ATP indicate that the herbicides are bonded through the metal component of the enzyme, similar to the nicotinamide part of NAD. The interaction constant less than unity found for the herbicide-ATP system indicates that the bonding site in the active center of the enzyme is different for the herbicides and the adenine part of NAD.