Action kinetics of the inhibition of nitrate reductase of rice plants

Abstract

By using affinity chromatography and Sephadex G-200 chromatography two molecular forms of a nitrate reductase inhibitor from foot extracts of rice seedlings were separated. One inhibitor had a molecular weight of 46000. The other had a molecular weight of 240000 and appeared to be a complex of inhibitor and nitrate reductase. Both free and bound forms of the inhibitor inactivated nitrate reductase activity with similar reaction kinetics. The inactivation consisted of two steps: the inhihitor first binds with nitrate reductase to cause a reduction in both NADH: nitrate reductase and reduced benzyl viologen: nitrate reductase activities. In the second phase, there is a complete inactivation of NADH:nitrate reductase after about 20 min. Reduced benzyl viologen: nitrate reductase activity was not affected by the second phase of inactivation.