Studies on the mechanism of electron transport to nitrogenase in Azotobacter vinelandii.

The involvement of the cytoplasmic membrane in electron transport to nitrogenase has been studied. Evidence shows that nitrogenase activity in Azotobacter vinelandii is coupled to the flux of electrons through the respiratory chain. To obtain information about proteins involved, the changes occurring in A. vinelandii cells transferred to nitrogen-free medium after growth on NH4Cl (depression of nitrogenase activity) were studied. Synthesis of the nitrogenase polypeptides was detectable 5 min after transfer to nitrogen-free medium. No nitrogenase activity could be detected until t = 20 min, whereupon a linear increase of nitrogenase activity with time was observed. Synthesis of nitrogenase was accompanied by synthesis of flavodoxin II and two membrane-bound polypeptides of Mr 29,000 and 30,000. Analysis with respect to changes in membrane-bound NAD(P)H dehydrogenase activities revealed the induction of an NADPH dehydrogenase activity, which was not detectable in membranes isolated from cells grown in the presence of NH4OAc. This induced activity was associated with the appearance of a polypeptide of Mr 29,000 in the NADPH dehydrogenase complex.