Nitrogenases molybdenum-dependent

METHOD OF CONTINUOUS VARIATION MOLYBDENUM COFACTOR (MoCo) Molybdenum-dependent reactions, ALDEHYDE OXIDASE MOLYBDOPTERIN NITRATE REDUCTASE NITROGENASE SULFITE OXIDASE XANTHINE DEHYDROGENASE MOLYBDOPTERIN... 

Newton, W.E., Fisher, K., Kim, C.-H., Shen, J, Cantwell, J.S., Thrasher, K S., and Dean, D.R. (1995) Probing catalytic function through amino-acid substitutions in Azotobacter vinelcmdii molybdenum-dependent nitrogenase. Curr. Plant Sci. Biotechnol. Agric. 27 (Nitrogen Fixation Fundamentals and Applications), 91-96. 

These enzymes are somewhat less active toward N2 than the molybdenum-dependent nitrogenase. However, recall that (i) protein dissociation is usually rate limiting, and (ii) proton reduction competes with nitrogen reduction. Therefore, it is likely that the activation barriers are similar for nitrogen reduction by the different nitrogenases. There is high sequence homology (and invariably... 

Coupling the results from the Mo model complex [57] with the explanation for the presence and possible action of homocitrate, these results provide the best model to date for N2 reduction by conventional molybdenum nitrogenases. Vanadium-dependent nitrogenases probably undergo similar reactions, but iron-only nitrogenases [66] and the unique molybdenum-dependent nitrogenase from Streptomyces thermoautrophicus [67] present further mysteries. 

In 1930, Hermann Bortels (1902-1979) recognised that nitrogen fixation is a molybdenum-dependent process. Obviously, the nitrogenases from Rhizobium meliloti, Azotobacter vinelandii and Clostridium pasteurianum have a similar constitution. In 1966, Leonard E. Mortenson identified for the first time an Fe- and a MoFe-protein as parts of the nitrogenase enzyme system. The exact structure of the nitrogenase-molybdenum-iron protein from Azotobacter vinelandii [28] was clarified in 1992, and that from Clostridium pasteurianum [29] in 1993, both by Douglas C. Rees. [30] The Fe-protein is a y2-dimer with a molar mass of some 60,000 Daltons, and the MoFe-protein is an ca. 

A preparation of the third nitrogenase from A. vinelandii, isolated from a molybdenum-tolerant strain but lacking the structural genes for the molybdenum and vanadium nitrogenases, was discovered to contain FeMoco 194). The 8 subunit encoded by anfG was identified in this preparation, which contained 24 Fe atoms and 1 Mo atom per mol. EPR spectroscopy and extraction of the cofactor identified it as FeMoco. The hybrid enzyme could reduce N2 to ammonia and reduced acetylene to ethylene and ethane. The rate of formation of ethane was nonlinear and the ethane ethylene ratio was strongly dependent on the ratio of nitrogenase components. 

Information, particularly structural, concerning vanadium-dependent nitrogenases, is relatively limited. The consensus is that they resemble the molybdenum nitrogenase in most aspects except for the presence of a FeV cofactor, and they will not be discussed further. 

The most extensively studied nitrogenase enzyme contains two kinds of transition metals, that is, iron and molybdenum, and is called molybdenum nitrogenase. In growth conditions where molybdenum concentration is low, a nitrogenase depending on iron and vanadium is expressed. ... 

Molybdenum has long been known to have a role in nitrogen fixation over 50 years ago Bortels showed that Mo stimulated the N2-dependent growth of Azotobacter (2). Subsequently, these observations were rationalized when all purified nitrogenases were shown to be separable into an Fe protein and a MoFe protein that contained Mo as part of an essential iron- and molybdenum-containing cofactor (Fe-Moco), the probable site at which N2 is reduced. 

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