Nitrogenase enzymes reactions

These were relatively low-resolution structures, and with refinement some errors in the initial structural assignments have been detected (4-7). Since the structures were first reported the subject has been extensively reviewed in this series (8) and elsewhere 9-15). This review will focus on the structure, biosynthesis, and function of the met-allosulfur clusters found in nitrogenases. This will require a broader overview of some functional aspects, particularly the involvement of MgATP in the enzymic reaction, and also some reference will be made to the extensive literature (9, 15) on biomimetic chemistry that has helped to illuminate possible modes of nitrogenase function, although a detailed review of this chemistry will not be attempted here. This review cannot be fully comprehensive in the space available, but concentrates on recent advances and attempts to describe the current level of our understanding. 

At the same time, this redox lability makes Mo well suited as a cofactor in enzymes that catalyze redox reactions. An example is the prominence of Mo in nitrogen fixation. This prokaryotic metabolism, the dominant pathway for conversion of atmospheric Nj to biologically-useful NH, utilizes Mo (along with Fe) in the active site of the nitrogenase enzyme that catalyzes Nj reduction. Alternative nitrogenases that do not incorporate Mo have been identified, but are markedly less efficient (Miller and Eady 1988 Eady 1996). 

This mechanism illustrates another putative role for the hydron in nitroge-nase—as a catalyst for product release. It further illustrates the restrictions in defining a mechanism for substrate conversion by investigating only the enzyme reaction. The involvement of hydrons in the reactions of the nitrogenases can only be inferred from the consumption of electrons, and key catalytic roles for hydrons will not be evident. 

Search the BRENDA database and find information on the enzymes EC 1.13.12.14, azobenzene reductase, and nitrogenase. What reactions do those enzymes catalyze What are their optimum p H and temperature operating ranges And what are their typical TOFs ... 

Oxidized forms of DIN (NC>3 and NO2-) must also be converted into ammonia by either nitrate or nitrate reductases before being fixed into organic matter. Similarly, there is a nitrogenase reductase reaction involved in the fixation of N2. The range of fractionation observed with NC>3 assimilation is similar to that observed with NH4+, with more fractionation (by diatoms) occurring with higher ambient NO3 concentrations (Wada and Hattori, 1978). Active transport of NC>3 has been observed by marine diatoms however, details of the membrane-bound enzyme involved with this reaction remain unclear (Falkowski, 1975 Packard, 1979). 

The two-component Mo-nitrogenase enzyme catalyzes the reduction of N2 to 2NH4 + as its physiological reaction. Concomitant with the reduction of N2, H2 evolution occurs, with electrons supplied by the same reductants that reduce N2. The limiting stoichiometry appears to be... 

The nitrogenase enzyme complex found in nitrogen-fixing bacteria catalyzes the production of ammonia from molecular nitrogen. The half-reaction of reduction (Figure 23.2a) is... 

The nitrogenase enzyme found in root nodules of leguminous plants catalyzes crucial reactions in nitrogen fixation. 

The Nitrogenase enzyme complex is not only specihc to reduction of dinitrogen, but also reduces acetylene (C2FI2) to ethylene (C2FI4). This reaction requires the transfer of two electrons. 

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