Nitrogen assimilation

Lowe, D. J. Mitchell, C. In Nitrogen Assimilation Molecular and Genetic Aspects Abstracts, University of South Florida, 1997. 

B. Botton and M. Chalot, Nitrogen assimilation Enzymology in ectomycorrhizas, Mvcorrhiza Structure, Molecular Biology and Function (A. K. Varma and B. Hock, eds.), Springer-Verlag, Berlin Heidelberg, New York, 1995, pp. 325-364. 

Table 2.3 Naturally observed isotope fractionation for nitrogen assimilation (after Fogel and Cifuentes Fogel and Cifuentes 1993)...

Nixon, B.T. Ronson, C.W. Ausubel, F.M. Two-component regulatory systems responsive to environmental stimuli share strongly conserved domains with the nitrogen assimilation regulatory genes ntrB and ntrC. Proc. Natl. Acad. Sci. USA, 83, 7850-7854 (1986)... 

Nitrogen Assimilation. Nitrogen assimilation is the uptake and metabolic use of N by plants and soil microbes (Figure 1). Assimilation by the terrestrial ecosystem controls the form of N eventually released into surface waters, as well as affecting the acid-base status of soil and surface waters. 

Verma, D.P.S. (1989). Plant genes involved in carbon and nitrogen assimilation in root nodules. In Plant Nitrogen Metabolism, ed. J.E. Poulton, T. Romeo E.E. Conn, pp. 43-63. New York Plenum Press. 

Raven, J. A., and Smith, F. A. (1976). Nitrogen assimilation and transport in vascular land plants in relation to intracellular pFl regulation. New Phytol. 76,415 431. 

Sessi, E., Nardi, S., and Gessa, C. (2000). Effects of low and high molecular weight humic substances from two different soils on nitrogen assimilation pathway in maize seedlings. Humic Subst. Environ. 2(1/4), 39 16. 

There were 37 distinct enzymes that contain molybdenum or tungsten known by the end of 1997. The enzymes are diverse in function, broadly distributed, and include oxidases, reductases, dehydrogenases, a transhydroxylase, and a hydratase. The Mo enzymes are found in eubacteria, archae, protista, fungi, plants, and animals (including humans) and are essential for respiration and carbon and nitrogen assimilation. Several of the enzymatic substrates and products are key components in the nitrogen, sulfur, selenium, carbon, and arsenic cycles and have major biological and environmental impact. 

The potentials found for nitrate reductases [96] vary with the role of the particular enzyme. Assimilatory nitrate reductase, found in plants, algae, and fungi, is involved in the first step in nitrogen assimilation and has a molybdenum center that operates at around 0 mV. Respiratory (dissimilatory) nitrate reductase, utilized by bacteria in energy yielding processes, has a molybdenum center that operates at around +200 mV [97,98],... 

Callies, R Altenburger, R., Abarzua, S Mayer, A., Grimme, L.H., Leibfritz, D. (1992). In situ nuclear magnetic resonance of 15N pulse labels monitors different routes for nitrogen assimilation. Plant Physiol. 100, 1584-1586. 

Ammonia is toxic at high concentrations, even though ammonium ion, NH4+ is an intermediate in many reactions. For its utilization, ammonia must be incorporated into organic forms, transferred, and then incorporated into other compounds, for example, amino acids and nucleotides. The amino acids glutamine and glutamate and the compound carbamoyl phosphate are the key intermediates of nitrogen assimilation, leading to different classes of compounds. 

Fig. 1. Redox metabolism in Saccharomyces cerevisiae during anaerobic growth on glucose. The ethanol yield is lowered by the production of biomass and glycerol. The glycerol flux, x, can be decreased, and the ethanol yield thereby increased if the stoichiometric coefficient a for biomass formation is reduced, e.g., by having nitrogen assimilation via an NADH-depen-dent glutamate dehydrogenase [10]...

By replacing the NADH-dependent glutamate dehydrogenase, which is the major nitrogen assimilation route in S. cerevisiae, the NADH formation associated with biomass synthesis was reduced, i. e., the stoichiometric coefficient a in Fig. 1 was reduced. 

Other reactions leading to NH4 removal from soil solution besides microbial nitrogen assimilation, metal-ammine formation, or adsorption onto mineral surfaces, involve NH3 fixation by incorporating it as NH2 in aromatic rings of humic acids (quinone) followed with aromatic ring condensation. 

All plants depend on nitrate reductase to accomplish the seemingly trivial reaction of nitrate reduction to nitrite, often the first step of nitrogen assimilation into compounds required for growth (5, 22). Many bacteria use molybdenum or tungsten enzymes in anaerobic respiration where the terminal electron acceptor is a reducible molecule other than oxygen, such as nitrate (2, 50), polysulfide (51), trimethylamine oxide (33, 52) or dimethyl sulfoxide (DMSO) (2, 29, 30). 

Nitrate reductases (14) are found in a wide range of eukaryotes and prokaryotes and have a crucial role in nitrogen assimilation (33, 34) and dissimilation (35). These reductases catalyze the reduction of NO3 to N02. For the assimilatory nitrate reductases this reaction is followed by... 

Elmerich, C. (2001) Nitrogenase biochemical, molecular and genetic aspects, Nitrogen Assimilation by Plants 149-167. 

Rather that interfering with methionine metabolism, T-3-L is a specific, site-directed inhibitor of glutamine synthetase (GS), a critical enzyme for nitrogen assimilation (12). The widespread... 

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