Nitrate reductase properties

It is not clear why some organisms have two 14-3-3 isoforms while others have up to 12. Binding 14-3-3 inhibits the plant enzyme nitrate reductase and there appears to be no selectivity between plant 14-3-3 isoforms in fact yeast and human isoforms appear to work equally as well in vitro. The best example where selectivity has been demonstrated is human 14-3-3o. 14-3-3o Preferential homodimerizes with itself and crystallization revealed a structural basis for this isoform s dimerization properties as well as for its specific selectivity for target binding proteins. Here partner specificity is the result of amino acid differences outside of the phosphopeptide-binding cleft. 

Moreno-Vivian C, P Cabello, M Martmez-Luque, R Blasco, F Castillo (1999) Prokaryotic nitrate reduction molecular properties and functional distinction among bacterial nitrate reductases. J Bacteriol 181 6573-6584. 

L. P. Solomonson and M. J. Barber, Assiinilatory nitrate reductase functional properties and regulation. Aimu. Rev. Plant Physiol. Mol. Biol. 41 225 (1990). 

The redox properties of Mo also make it useful in enzymes that catalyze reactions involving two-electron or oxygen-atom transfer (Frausto da Silva and Williams 2001). Such enzymes include nitrate reductase, sulfite oxidase, formate dehydrogenase and aldehyde oxidase (Hille 1996 Stiefel 1997 Kroneck and Abt 2002). Hence, while Mo is rarely a terminal electron... 

Carlson, C. A., Ferguson, L. P., and Ingraham, J. L. (1982). Properties of dissimilatory nitrate reductase purified from the denitrifier Pseudomonas aeruginosa. J. Bacteriol. 151, 162-171. 

Craske, A., and Ferguson, S. J. (1986). The respiratory nitrate reductase from Paracoccus denitrificans. Molecular characterization and kinetic properties. Eur.. Biochem. 158, 429-436. 

Forget, P. (1971). Les nitrate-reductases bacteriennes. Solubilisation, purification, et properties de I enzyme A de Micrococcus denicrificans. Eur. ]. Biochem. 18, 442-450. 

Bacterial assimilatory nitrate reductases have similar properties.86/86a In addition, many bacteria, including E. coli, are able to use nitrate ions as an oxidant for nitrate respiration under anaerobic conditions (Chapter 18). Tire dissimilatory nitrate reductases involved also contain molybdenum as well as Fe-S centers.85 Tire E. coli enzyme receives electrons from reduced quinones in the plasma membrane, passing them through cytochrome b, Fe-S centers, and molybdopterin to nitrate. The three-subunit aPy enzyme contains cytochrome b in one subunit, an Fe3S4 center as well as three Fe4S4 clusters in another, and the molybdenum cofactor in the third.87 Nitrate reduction to nitrite is also on the pathway of denitrification, which can lead to release of nitrogen as NO, NzO, and N2 by the action of dissimi-latory nitrite reductases. These enzymes873 have been discussed in Chapters 16 and 18. 

Solomonson, L.P. Barber, M.J. (1990). Assimilatory nitrate reductase functional properties and regulation. Annual Review of Plant Physiology and Plant Molecular Biology 41, 225-53. 

Unlike the nitrogenases, which do not vary much in composition and physical properties with the source, nitrate reductases vary considerably from one organism to the next. The only feature which they all seem to have in common is an absolute requirement for the presence of molybdenum. 

In a further development of this research (84), the reaction of [Mo(CO)2(S2C2R2)2] with the nucleophiles R Y- (R = Ph, z-Pr, or C6FsO, Y = O R = 2-Ad Y = O, S or Se) (see Fig. 10) was shown to form the corresponding des-oxo MoIV( YR )(S2C2Me2)21 complex. These complexes have considerable potential as structural analogues for the reduced forms of the catalytic centers of the DMSOR and the TMAOR (Y = O), the dissimilatory nitrate reductase (Y = S), and the formate dehydrogenase (Y = Se) (13). Thus, the spectroscopic and electrochemical properties and reactivity of these complexes will provide useful calibrations of the corresponding behavior of the catalytic centers of the MPT enzymes. 

The nitrate reductase from Haloferax denitrificans was purified to electrophoretic homogeneity aided by the ease with which the enzyme is solubilized from membranes and the stability of the reductase in solutions of low ionic strength [142]. The enzyme is composed of two subunits that resemble the a and (3 subunits of the dissimilatory nitrate reductases found in bacteria [143]. Dissimilatory nitrate reductases have a third subunit that contains a b-type cytochrome. No such subunit is detected in the nitrate reductase from H. denitrificans. However, this observation has no significance since this subunit is often lost during purification. The most striking property of the enzyme is its response to salt concentration, both when membrane-bound [144] and following purification [142]. Nitrate reduction is most active in the absence of added salt and the enzyme is stable for weeks on end in the absence of salt. Similar nitrate reductase activities occur in... 

Labeyrie et al. (41) isolated a trypsin fragment of 11 kDa from S. cerevisiae flavocytochrome 62 that contained heme but was devoid of flavin and had no lactate dehydrogenase activity. The fragment, which was referred to as cytochrome 62 core, was found to have spectral properties very like those of microsomal cytochrome 65 (41). This similarity with cytochrome 65 is borne out by comparisons of amino acid sequence (42-44). The sequence similarity extends to related heme domains of sulfite oxidase (45, 46) and assimilatory nitrate reductase (47). The existence of a protein family with a common cytochrome 65 fold was suggested by Guiard and Lederer (48) and this is supported by the close similarity between the three-dimensional structures of microsomal cytochrome 65 (49) and the cytochrome domain of flavocytochrome 62 (23-25). 

Although the hypothesis of Egami may be an oversimplification, it is certainly true that Fe is widely used in redox systems. Zn" in hydrolysis, esterification, and. similar reactions, and molybdenum in nitrogenase, xanthine oxidase, nitrate reductase, etc. Pulling abundance aside, discuss the specific chemical properties of these metals that make them well suited for their tasks. 

Garrett RH, Nason A. 1969. Further purification and properties of Neurospora nitrate reductase. J Biol Chem 244 2870-2882. 

Chaudhry GR, MacGregor CH (1983) Cytochrome b from Escherichia coli nitrate reductase. Its properties and association with the enzyme complex. J Biol Chem 258 5819-5827 Chaudhry GR, Suzuki I, Lees H (1980) Cytochrome oxidase of Nitrobacter agilis isolation by hydrophobic chromatography. Can J Microbiol 26 1270-1274 Chaudhuri SK, Lack JG, Coates JD (2001) Biogenic magnetite formation through anaerobic biooxidation of Fe(II). Appl Environ Microbiol 67 2844—2848 Cheeseman P, Toms-Wood A, Wolfe RS (1972) Isolation and properties of a fluorescent-compound, Factor 420, from Methanobacterium strain M.o.H. J Bacteriol 112 527-531... 

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