Nitrogenase: A nucleotide-dependent molecular switch
In the simplest terms, the biological nitrogen cycle is the reduction of atmospheric dinitrogen (N2) to ammonia with the subsequent reoxidation ammonia to dinitrogen (1). At the reduction level of ammonia, nitrogen incorporated into precursors for biological macromolecules such as proteins and nucleic acids. Reoxidation of ammonia to dinitrogen ("denitrification") by a variety of microbes (by way of nitrite and other oxidation levels of nitrogen) leads to the depletion of the "fixed," biologically usable, nitrogen pool. Besides the relatively small contribution from commercial ammonical fertilizer production, replenishing of the nitrogen pool falls mainly to a limited number of physiologically diverse microbes (e.g. eubacteria and archaebacteria; free-living and symbiotic; aerobic and anaerobic) that contain the nitrogenase enzyme system.
"Reprinted, with permission, from the Annual Review of Biochemistry, Volume 63 copyright 1994 by Annual Reviews, www.annualreviews.org" The efforts and contributions of J. Kim, M. Georgiadis, D. Woo, M. K. Chart, M. W. Day, J. Schlessman, H. Komiya, L. Joshua-Tot, M. H. B. Stowell, B. T. Hsu and A. J. Chirino are deeply appreciated, as are discussions, sharing of preprints, etc with our nitrogenase colleagues. Research in the authors' laboratories was supported by grants from NIH and NSF.