ELECTRON-TRANSPORT TO NITROGENASE IN RHODOSPIRILLUM-RUBRUM - THE ROLEOF NAD(P)H AS ELECTRON-DONOR AND THE EFFECT OF FLUOROACETATE ON NITROGENASE ACTIVITY

The role of the reactions of the TCA cycle in the generation of reduct ant for nitrogenase in Rhodospirillum rubrum has been investigated. Ad dition of fluoroacetate inhibited nitrogenase activity almost complete ly when pyruvate or endogenous sources were used as electron donors, w hereas the inhibition was incomplete when malate, succinate or fumarat e were used. Addition of NAD(P)H to cells supported nitrogenase activi ty, both with and without prior addition of fluoroacetate. We suggest that the role of the TCA cycle in nitrogen fixation in R. rubrum is to generate reduced pyridine nucleotides which are oxidized by the compo nents of the electron transport pathway to nitrogenase.