Nitrate reductase types

Nitrate reductases have been isolated from bacteria, plants and fungi and always contain molybdenum. Two types may be distinguished (a) the assimilatory nitrate reductases which catalyze the reduction of nitrate to nitrite, which ultimately is reduced to ammonia and used by... 

Pseudomonas aeruginosa can synthesize both types of nitrate reductase, depending upon the environmental conditions, the dissimilatory enzyme being repressed by dioxygen.1049... 

E. coli uses nitrate as a terminal electron acceptor through a respiratory, dissimilatory nitrate reductase whose synthesis is induced when nitrate is provided, and which is repressed by oxygen. Nitrate reductase is discussed with other molybdoenzymes in Section 62.1.9, and catalyzes the reduction of nitrate to nitrite. The enzyme is isolated from the cytoplasmic membrane of E. coli, and contains three subunits (a, j8 and y) although the y-subunit may be absent in some preparations. The -y-subunit is a b-type cytochrome, and the a-subunit is reported to be the catalytic subunit. The enzyme contains a number of iron-sulfur clusters, including a HiPIP and at least two ferredoxins.1054,1437... 

Streit, L., Martin, B.A. Harper, J.E. (1987). A method for the separation and purification of the three forms of nitrate reductase present in wild-type soybean leaves. Plant Physiology 84, 654-7. 

Vaucheret, H., Chabaud, M., Kronenberger, J. Caboche, M. (1990). Functional complementation of tobacco and Nicotiana plumbagini-folia nitrate reductase deficient mutants by transformation with the wild-type alleles of the tobacco structural genes. Molecular and General Genetics 220, 468-74. 

The assimilatory enzyme from the mold Neurospora crassa has been intensively studied for over two decades, particularly by Nason and his collaborators. Thus, Nason and Evans (39) identified FAD as a prosthetic group in the enzyme Nicholas, Nason, and McElroy (40) showed that molybdenum was required for the synthesis of nitrate reductase Nicholas and Nason (41) suggested its presence in the enzyme Garrett and Nason (42) showed that a b-type cytochrome (cytochrome 6557) co-purifies with this nitrate reductase and Nason et al. (11) suggested, from in vitro complementation experiments with nitrate reductaseless mutants, that the enzyme consists of at least two components required for activity. These workers have suggested that the electron transfer pathway is ... 

Verbeet, M.Ph., and Groenen, E.J.J. (2001) A single-crystal electron paramagnetic resonance study at 95 GHz of the type 1 cooper site of the green nitrate reductase of Alcaligenesfeacali, s J. Phys. Chem. B 105,... 

Ratnam, K., Shiraishi, N., Campbell, W. H., and Hille, R., 1995, Spectroscopic and kinetic characterization of the recombinant wild-type and C242S mutant of the cytochrome b reductase fragment of nitrate reductase, J. Biol. Chem. 270 24067924072. 

Two types of dissimilatory nitrate reductases, localized in either the cytoplasmic membrane or the periplasm, are widespread among bacteria. The cytoplasmic membrane-bound nitrate reductase (Nar) catalyzes the first steps of denitrification (NOs" N02 NO N2O... 

The molybdenum-containing oxidoreductases that catalyze Eq. (1) have been variously termed molybdenum hydroxylases (6), oxotransferases (7), and oxo-type molybdenum enzymes (8). Molybdenum hydroxylase aptly describes the conversion of xanthine to uric acid, but the name seems less appropriate for the reactions catalyzed by sulfite oxidase and nitrate reductase oxotransferase implies that the function of these enzymes is to transfer oxo groups, even though relatively little is known about their actual mechanism of action and the name oxo-type molybdenum enzyme recognizes both the apparent oxo transfer chemistry of Eq. (1) and the fact that the molybdenum atom in each of these enzymes contains at least one terminal oxo group. In this chapter, we shall refer to these enzymes as pterin-containing molybdenum enzymes because a 6-substituted pterin appears to be a common chemical feature of all of the 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... 

Many type b cytochromes associated with the classic cytochrome oxidase (a and 03) show their a peaks at 561-563 nm, and they are usually designated as cytochrome b. The name cytochrome 61 was originally used for the pigments with a peak at 557-560 nm, but it is now generally applied to the cytochrome in the nitrate reductase system. Cytochrome 62 (a, 557 nm) is the entity of yeast lactate dehydrogenase which contains FMN and protoheme. Cytochromes 63 (a, 559 nm) and 65 (a, 556 nm) participate in the microsomal electron transport system in plants and animals, respectively. Both the primary and ternary structures of cytochrome 65 are known. Cytochromes bg (a, 563 nm) and 6-559 are the components of the photosynthetic electron transport system in plant. 

The name cytochrome fei has been used for the bacterial type b cytochromes having the a band near 560 nm since its designation by Keilin (193). However, this name is now usually applied in a limited sense to the cytochromes with a band at 558 or 559 nm in the nitrate reductase (nitrate respiration) system, which is a more primitive form of respiration than the mitochondrial respiration system. 

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