THE MO-BASED, V-BASED, AND FE-BASED NITROGENASE SYSTEMS OF AZOTOBACTER

Azotobacter species have been shown to have three genetically distinct nitrogenase systems, one based on molybdenum(Mo) similar to nitrogenase isolated from a wide range of N2 fixing organisms, one based on vanadium(V), and a third that contains iron(Fe) but only low levels of Mo or V. The apparently essential role of Mo was further supported by subsequent developments in the genetics of nitrogen fixation. These showed that genes involved in Mo uptake the FeMoco synthesis were closely linked and often coregulated with the genes for the structural polypeptides of Mo nitrogenase, the amino acid sequences of which had been highly conserved in evolution. In addition, kinetic studies on the mechanism of N2 reduction by Mo nitrogenase and the reactivity of N2 and likely reduction intermediates at Mo- or W-containing centers provided a plausible scheme for N2 reduction by nitrogenase. © 1991 Academic Press, Inc.