Nitrogen fixation enzyme nitrogenase

Recently we have attempted to pursue multi-electron fixation processes as models for N2 or CO2 fixation. In nature, the N2-fixation enzyme, nitrogenase, exhibits non-specificity properties, and acetylene competes for nitrogen as the fixation substrate (21). The fixation process of acetylene to methane and of nitrogen to ammonia (euqations 14 and 15) have several common features (i) both involve the cleavage of a triple bond (ii) the two reactions involve 6 electrons in the fixation mechanism. Thus, it seems that the photocleavage of acetylene to methane might offer a good model for development of -fixation cycles (22). 

Currently accepted mechanism for nitrogen fixation by nitrogenase enzymes... 

In nature, nitrogen fixation is accomplished by nitrogenase, an enzyme that binds N2 and weakens its bonding sufficiently to break the triple bond. Only a few algae and bacteria contain nitrogenase. Our Chemishy and Life Box describes what is known about this enzyme. 

In Nature, nitrogen fixation is mediated by the enzyme nitrogenase according to Eq. (1) (6)... 

Molybdate, although present in small amounts in soil, is an essential nutrient for nitrogen fixation, specifically in the enzyme nitrogenase. It does not move readily through soil and is therefore considered to be of limited mobility. 

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). 

In marked contrast to the conditions under which nitrogen is converted to ammonia in the laboratory, in nature atmospheric N2 is converted to ammonia under the mildest of conditions by enzymes called nitrogenases in a process termed nitrogen fixation. This example testifies to the power of enzymes, about which much more follows in chapter 9. 

The biological nitrogen fixation process is Introduced. Discussion focusses on the Dominant Hypothesis of nitrogenase composition and functioning. The enzyme system catalyzes the six-electron reduction of N2 to 2 NH3 concomitant with the evolution of H2. ATP hydrolysis drives the process. The two protein components of the enzyme,... 

The process of nitrogen fixation is an essential part of the nitrogen cycle on the planet earth(l). It is estimated that greater than 60Z of the N2 that is ultimately converted to NH4+ is done so by the nitrogenase enzyme system. The availability of fixed nitrogen is often the limiting factor in plant growth( ). To... 

---