Effect of NH4+ on nitrogenase activity in nodule breis and bacteroides from Pisum sativum L

Nodule breis and bacteroid preparations were made from Pisum sativum L. (cv. Trapper) inoculated with a single strain of Rhizobium leguminosarum. The detached nodules were triturated under helium flow. The resultant breis could support C2H2 reduction in N-Tris[hydroxymethyl]methyl-2-aminoethane-sulfonic acid buffer (Tes) without any additions for over an hour. NH4+ was found to inhibit C2H2 reduction and H2 evolution. The inhibition was not dependent on the counterion and was evident immediately after the addition of NH4+ to the reaction mixture. L-Methionine-D,L-sulfoximine, added to inhibit assimilation of NH4+, had no effect on the inhibition. Addition of pyruvate enhanced the rate of C2H2 reduction in breis and partially overcame the inhibition of NH4+. Pyruvate was found necessary for measurable activity in bacteroid preparations. When ATP and an ATP-generating system were used in breis the effect of NH4+ was not observed.