Nitrogen reduction

Nitrogen uptake that results in the formation of new biomolecules is termed an assimilation process, such as assimilatory nitrogen reduction. The processes that result in the release of DIN into seawater are referred to as dissimilations, such as dissimi-latory nitrogen reduction. An example of the latter is denitrification, in which nitrate and nitrite obtained from seawater serve as electron acceptors to enable the oxidation of organic matter. This causes the nitrate and nitrite to be transformed into reduced species, such as N2O and N2, which are released back into seawater. 

The biogeochemical cycling of nitrogen is very much controlled by redox reactions. This perspective is presented in Figure 24.3 for the redox reactions that take place in the water column and sediments. The major pathways of reduction are nitrogen fixation, assimilatory nitrogen reduction, and denitrification. The major oxidation processes are nitrification and anaerobic ammonium oxidation (anammox). Each of these is described next in further detail. 

Dissimilatory nitrogen reduction tends to be a sequential process in which the end products are the gases N2 and N2O. Conversion of DIN to N2 and N2O removes fixed nitrogen from the ocean. This is the major route by which nitrogen is removed from the sea as burial of fixed nitrogen in the sediments is minor (see Figure 24.2). 

Like assimilatory nitrogen reduction, denitrification proceeds through a series of steps with nitrate first being reduced to nitrite, followed by reduction of nitrite to N2(g). Under some conditions, N20(g) is also produced. 

Copper is an essential element. Copper plays a significant role in several physiological processes - photosynthesis, respiration, carbohydrate distribution, nitrogen reduction and fixation, protein metabolism, and cell wall metabolism. Many plant metalloenzymes contain copper. It also influences water permeability of xylem vessels and thus controls water relationships. It is mainly complexed with organic compounds of low molecular weight and with proteins (Henze and Umland, 1987). Kabata-Pendias and Pendias (1984) have compiled data on the Cu concentrations in... 

We believe that these studies are important for the design of non-molybdenum based catalytic complexes for nitrogen reduction. 

Nitrogen Fixation in Nature The nitrogenase enzyme is a two-component protein that consists of an electron-transfer Fe protein and a catalytic protein [85]. Three different nitrogenase enzymes are known, which differ primarily in the nature of the putative active site within the catalytic protein. The most common form is the MoFe protein, in which the active site for nitrogen reduction, the so-called FeMo cofactor (FeMoco), is composed of seven irons, one molybdenum, and nine sulfides... 

Dzhabiev, T.S., Mironova, S.A., and Shilov, A.E. (1999) Kinetic evidence of nitrogen reduction in the coordination sphere of a polynuclear complex, Kinetics and Catalysis (Translation of Kinetika i Kataliz) 40, 764-768. 

Nitrogen reduction Nitrogenase has been a model system for studying general principles involving electron... 

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