Nitrite and nitric oxide as inhibitors of nitrogenase from soybean bacteroids.

Nitrite was able to strongly inhibit C(2)H(2) reduction by nitrogenase from soybean bacteroids, whereas H(2) evolution was unaffected under the same conditions. NO inhibited both C(2)H(2) reduction and H(2) evolution; during C(2)H(2) reduction, sensitivity of nitrogenase to NO was higher than to NO(2), and the K(i) values were, respectively, 0.056 and 0.52 mM. Production of NO resulting from a reduction of NO(2) by dithionite in nitrogenase incubations was observed. However, the characteristics of inhibitions and the low level of NO generated by nitrite reduction ruled out the suggestion concerning a direct role of NO to explain the inhibitory effect of NO(2) on nitrogenase.