Nitrogenase mechanisms

Syrtsova, L.A., Druzhinin, S. Yu., Khramov, A. V., and Moravsky, A.P. (1995) Photostimulation of nitrogenase reaction in vitro for investigation of nitrogenase mechanism action Curr. Plant Sci. Biotechnol. Agric. 27 (Nitrogen Fixation Fundamentals and Applicaaaation. 

It should be emphasized that the above discussed model reactions are not only relevant for a better understanding of the nitrogenase mechanism, but even more important, they could open a door for new technologies of mild -N2-fixation (see e.g. Ref.169 ). 

Non-enzvmatic simulation of nitrogenase reactions and the mechanism of biological nitrogen fixation. G. N. Schrauzer, Angew. Chem., Int. Ed. Engl., 1975, 14, 514-522 (36). 

Mr 220-250 kDa. Figure 1 shows an overall electron transfer pathway for the nitrogenases where the Fe proteins act as very specific, essential electron donors to the larger proteins. This is not the only role for the Fe proteins (see Section IV,C) and their role in the mechanism is almost certainly more complex than that of a simple electron transfer agent (see below. Section V). Electron transfer from the Fe protein to... 

A comprehensive description of the mechanism of molybdenum nitrogenase has been provided by the Lowe-Thorneley scheme 102) (Figs. 8 and 9). In this scheme the Fe protein (with MgATP) functions as a single electron donor to the MoFe protein in the Fe protein cycle (Fig. 8), which is broken down into four discrete steps, each of which may be a composite of several reactions ... 

Some aspects of the Lowe-Thomeley mechanism for nitrogenase action, which has served us well over the past 15 years, are being called into question. In particular, the necessity for protein-protein dissociation after each electron transfer, the rate-determining step with dithionite as reductant, is being questioned when the natural electron donor flavodoxin or other artificial systems are used. Some aspects of the mechanism should be reinvestigated. 

The dependence of rate constants for approach to equilibrium for reaction of the mixed oxide-sulfide complex [Mo3((i3-S)((i-0)3(H20)9] 1+ with thiocyanate has been analyzed into formation and aquation contributions. These reactions involve positions trans to p-oxo groups, mechanisms are dissociative (391). Kinetic and thermodynamic studies on reaction of [Mo3MS4(H20)io]4+ (M = Ni, Pd) with CO have yielded rate constants for reaction with CO. These were put into context with substitution by halide and thiocyanate for the nickel-containing cluster (392). A review of the chemistry of [Mo3S4(H20)9]4+ and related clusters contains some information on substitution in mixed metal derivatives [Mo3MS4(H20)re]4+ (M = Cr, Fe, Ni, Cu, Pd) (393). There are a few asides of mechanistic relevance in a review of synthetic Mo-Fe-S clusters and their relevance to nitrogenase (394). 

Barney, B.M., Lukoyanov, D., Yang, T.-C., Dean, D.R., Hoffman, B.M. and Seefeldt, L.C. (2006) A methyldiazene (NH=N-CH3)-derived species bound to the nitrogenase active-site FeMo cofactor implications for mechanism, Proc. Natl. Acad. Sci. U.S.A., 103, 17113-17118. 

Despite the availability of the molecular structures of the different active sites of the FeMo-nitrogenases, the mechanism of nitrogen fixation remains obscure. The interest of our discussion, however, is centred on the various modes proposed to describe how molecular nitrogen might coordinate the FeMoco. Some of the reported schemes are inspired by the type of coordination found in model compounds. 

It is likely that comparative structural and other studies of hydrogenases and nitrogenases will eventually illuminate events in the early evolution of energy-yielding mechanisms. We are indebted to the anaerobes for their necessary roles as recycling agents in Earth s element cycles. 

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