This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Yoch, D C Articles by Gotto, J W Search for Related Content PubMed PubMed Citation Articles by Yoch, D C Articles by Gotto, J W

Effect of light intensity and inhibitors of nitrogen assimilation on NH4+ inhibition of nitrogenase activity in Rhodospirillum rubrum and Anabaena sp.

ABSTRACT

Nitrogenase activity in Rhodospirillum rubrum was inhibited by NH4+ more rapidly in low light than in high light. Furthermore, the nitrogenase of cells exposed to phosphorylation uncouplers was inhibited by NH4+ more rapidly than was the nitrogenase of controls without an uncoupler. These observations suggest that high levels of photosynthate inhibit the nitrogenase inactivation system. L-Methionine-DL-sulfoximine, a glutamine synthetase inhibitor, prevented NH4+ from inhibiting nitrogenase activity, which suggests that NH4+ must be processed at least to glutamine for inhibition to occur. An inhibitor of glutamate synthase activity, 6-diazo-5-oxo-L-norleucine, inhibited nitrogenase activity in the absence of NH4+, but only in cells exposed to low light. The mechanism of 6-diazo-5-oxo-L-norleucine inhibition appeared to be the same as that induced by NH4+, because nitrogenase activity could be restored in vitro by activating enzyme and Mn2+. The inhibitor data suggest that the glutamine pool or a molecule that responds to it activates the Fe protein-modifying (or protein-inactivating) system and that the accumulation of this (unidentified) molecule is retarded when the cells are exposed to high light. It was confirmed here that Anabaena nitrogenase is also inhibited by NH4+, but only when the cells are incubated under low light. This inhibition, however, unlike that in R. rubrum, could be completely reversed in high light, suggesting that the mechanisms of nitrogenase inhibition by NH4+ in these two phototrophs are different.

This article has been cited by other articles:

• Zhang, Y., Wolfe, D. M., Pohlmann, E. L., Conrad, M. C., Roberts, G. P. (2006). Effect of AmtB homologues on the post-translational regulation of nitrogenase activity in response to ammonium and energy signals in Rhodospirillum rubrum. Microbiology 152: 2075-2089 [Abstract] [Full Text]