INVIVO INHIBITION OF NITROGENASE BY HYDROXYLAMINE IN RHODOSPIRILLACEAE - ROLE OF NITRIC-OXIDE

Rhodobacter capsulatus strains E1F1 and B10 and Rhodobacter sphaeroides DSM 158 did not use hydroxylamine as nitrogen source for growth but metabolized it mainly through the glutamine synthetase reaction. Hydroxylamine had a high toxicity for cells growing either under phototrophic or dark-aerobic conditions. L-methionine-D,L-sulfoximine partially inhibited hydroxylamine uptake and increased the inhibition time of nitrogenase activity by this nitrogen compound. Nitric oxide was also a powerful inhibitor of nitrogenase in intact cells of R. capsulatus. Since low amounts of NO were produced from hydroxylamine, short-term inhibition of nitrogenase in the presence of this compound could be mediated in vivo by nitric oxide.