Nitrate reductase location

The chlorate reductase has been characterized in strain GR-1 where it was found in the periplasm, is oxygen-sensitive, and contains molybdenum, and both [3Fe-4S] and [4Fe-4S] clusters (Kengen et al. 1999). The arsenate reductase from Chrysiogenes arsenatis contains Mo, Fe, and acid-labile S (Krafft and Macy 1998), and the reductase from Thauera selenatis that is specific for selenate, is located in the periplasmic space, and contains Mo, Fe, acid-labile S, and cytochrome b (Schroeder et al. 1997). In contrast, the membrane-bound selenate reductase from Enterobacter cloacae SLDla-1 that cannot function as an electron acceptor under anaerobic conditions contains Mo and Fe and is distinct from nitrate reductase (Ridley et al. 2006). 

Alefounder, P. R., and Ferguson, S. J. (1980). The location of dissimilatory nitrite reductase and the control of dissimilatory nitrate reductase by oxygen in Paracoccus denitri-ficans. Biochem.J. 192, 231-240. 

Many species of bacteria also have an assimilatory nitrite reductase which is located in the cytoplasm. There is relatively little known about such enzymes but the electron donor is throught to be NADPH and the active site again has siroheme (Cole, 1988). The assimilatory nitrite reductases of both plants and bacteria use nitrite that is provided as the product of the assimilatory nitrate reductases. Nitrate is a very common natural N source for plant and bacterial growth. 

This family includes the sulfite oxidases and dehydrogenases of prokaryotes Thiobacilli sp.), plants, birds, and animals, and the assimilatory nitrate reductases from bacteria, algae, fungi, and plants. The sulfite oxidases of higher eukaryotes are 100-110kDa homodimers (Table 1) they are located in the mitochrondrial intermembrane space and catalyze the oxidation of toxic sulfite to innocuous sulfate (equation 7). Human sulfite oxidase deficiency leads to major neurological abnormalities, mental retardation, dislocation of the ocular lenses, and early death. ... 

Canvin and Woo (1979) reported that under certain conditions Antimycin A (mitochondrial ATP site II inhibitor) was more effective in enhancing nitrite accumulation (75% of anaerobic control) by leaf discs than either amytal or rotenone (ATP site I inhibitors). In plant mitochondria, the malate dehydrogenase located on the outside of the inner membrane is capable of utilizing external NADH. They infer that in leaves under dark aerobic conditions, the mitochondria effectively compete with nitrate reductase for cytoplasmic NADH. Confirmation of this competition was afforded by a reconstituted system consisting of mitochondria, nitrate reductase, nitrate and NADH or NAD, malate, and malate dehydrogenase (Reed and Hageman, 1977). Nitrite production under aerobic conditions was 10% that observed under anaerobiosis. 

At least 12 genes are involved in the formation of nitrate reductase in various Enterobacteriaceae, 5 nar genes have been identified in Pseudomonas aeruginosa and 13 Chi mutations have been characterized in Bacillus licheniformis (Stouthamer, 1976). The physiological properties of chlorate-resistant mutants have been characterized and their location on the circular chromosome determined. Chi mutations have a pleotropic affect such characteristics as dehydrogenase activity, cytochrome distribution, and membrane protein composition may be influenced. The different Cfi/ mutants are able to synthesize various components of the complex nitrate reductase molecule. It is possible, in some instances, to form active enzyme by mixing components extracted from the appropriate mutants (Stouthamer, 1976). 

They suggested that the active pool could be located in the cytoplasm and the storage pool in the vacuole. Using comparable procedures, pool sizes of nitrate could not be measured in wheat leaves (Hageman et al., 1979a,b). These studies indicated that loss of nitrate reductase activity, diminishing supplies of reductant and other factors rather than lack of nitrate were responsible for the cessation of nitrite accumulation (used to indicate active pool size). It was concluded that the amount of nitrate in the cytoplasm was low and that nitrate was readily available from the apoplast (including the xylem elements). 

D. desulfuricans also showed a membrane-associated or soluble nitrate reductase catalyzing the respiratory reduction of nitrate to nitrite [ 134-136]. A cytochrome c-dependent nitrate reductase was also isolated from Geobacter metallireducens [137], Obviously, nitrate uptake and nitrite extrusion into the bulk phase is dispensable for periplasmic nitrate reductases. In addition, a periplasmic location of nitrate reductases will prevent the interaction of potentially toxic compounds such as nitrite or NO with cytoplasmic proteins. 

Regardless of whether the process of nitrate reduction is located in photosynthetic or nonphotosynthetic tissues, it still involves a cytoplasmically located nitrate reductase [reaction (6)] and a nitrite reductase complex [reaction (7)], which is located in plastids. Possible sources of reductant for these reactions have been discussed in several reviews (e.g., Lee, 1980 Abrol et al., 1983 Smirnoff and Stewart, 1985) and the conclusion reached that in heterotrophic (nonphotosynthetic) nitrate assimilation the NADH required by nitrate reductase might be derived from glycolysis, from the oxidative pentose phosphate pathway, or even from mitochondrial dehydrogenases (see I e, 1980), whereas the pentose phosphate pathway may be of singular significance in supplying NADPH for nitrite assimilation. As indicated for root tissue by Ernes et al. 

In 1%7, Miflin reported that a particulate fraction from pea or barley roots was able to reduce nitrite using reduced benzyl viologen as the electron donor. Miflin (1970) and Bourne and Miflin (1970) isolated a barley root particle that reduced nitrate to ammonia when provided with pyruvate and ATP. The fractionation techniques used separated the nitrosome from the mitochondrial and peroxisomal fractions. Dalling et al. (1972b) found that 15% of the total nitrite reductase activity of wheat roots was associated with an organelle that was tentatively identified as a proplastid. A proplastid location for nitrite reductase in tissue culture cells has been indicated by Washitani and Sato (1977a,b). 

Assimilatory nitrase reductases (ANR), which catalyze the reduction of nitrate to nitrite, subsequently converted to NH4 by nitrite reductase, are also members of this group [137,138]. The prototypic SO, an enzyme located in the mitochondrial intermembrane, catalyzes the biologically essential oxidation of sulfite to sulfate, the terminal reaction in the oxidative degradation of sulfur-containing methionine and cysteine amino acids. 

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