Reductases nitrate reductase

NITRATE REDUCTASE NITRATE REDUCTASE NITRENE NITRENIUM ION Nitric oxide,... 

Nitrate Reductase. Nitrate reductase is found widely distributed among plants and microorganisms and catalyzes the reduction of N03 to N02" (16,17,18,19). The physiological role of this enzyme depends... 

The two-domain, structural motif in FNR represents a common structural feature in a large class of enzymes that catalyze electron transfer between a nicotinamide dinucleotide molecule and a one-electron carrier. Beside the photosynthetic electron-transfer enzyme, others non-photosynthetic ones include flavodoxin reductase, sulfite reductase, nitrate reductase, cytochrome reductase, and NADPH-cyto-chrome P450 reductase. FNR belongs to the group of so-called dehydrogenases-electron transferases, i.e., flavoproteins that catalyze electron transfer from two, one-electron donor molecules to a single two-electron acceptor molecule. 

Nitrous oxide reductase Nitrate reductase + nitrite reductase + nitric oxide reductase... 

The first step, conversion of N03" to N02, is catalyzed by a large and complex enzyme called nitrate reductase. Nitrate reductase is a multi-subunit enzyme with Mr of about 800 kD. It contains bound FAD, molybdenum, and a cytochrome called cytochrome 557 (which contains an Fe4S4 complex). Nitrate reductase carries out the following reaction ... 

DM SO reductase Biotin-S-oxide reductase Trimethylamine-N-oxide reductase Nitrate reductase (dissimilatory) Formate dehydrogenase... 

Each step of the denitrification pathway is catalyzed by a distinct enzyme, nitrogen oxide reductase (nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase), that transfers electrons from the chain to the particular intermediate. Thermodynamically, in the absence of oxygen, nitrogen oxides are the most preferred electron acceptors by facultative bacterial groups. The role of nitrogen oxides in regulating organic matter decomposition has been discussed in earlier chapters (see Chapter 5). 

Nitrate Reductase. Nitrate reductase is a name applied to certain flavoproteins containing molybdenum that reduce nitrate to nitrite at the expense of reduced pyridine nucleotides. The enzyme from Neuro-spora requires TPNH, one from soybean leaves uses either TPNH or DPNH, while a preparation from the bacteria of soybean root nodules uses only DPNH. These enzymes require molybdenum and FAD. 

Nitrate Reductase. - Nitrate reductase is a molybdenum-containing... 

Molybdenum. Molybdenum is a component of the metaHoen2ymes xanthine oxidase, aldehyde oxidase, and sulfite oxidase in mammals (130). Two other molybdenum metaHoen2ymes present in nitrifying bacteria have been characteri2ed nitrogenase and nitrate reductase (131). The molybdenum in the oxidases, is involved in redox reactions. The heme iron in sulfite oxidase also is involved in electron transfer (132). 

Erythrityl is readily absorbed from the GI tract. It undergoes extensive first-pass metaboHsm ia the Hver by glutathione organic nitrate reductase. Time to onset of effect is 5—10 min by subHngual adrninistration and 20—30 min when swallowed. The duration of effects for the two routes ate up to 3 and 6 h, respectively. Adverse effects are similar to those described for nitroglycerin (99). 

Hemoprroteins contain heme Hemoglobin Cytochrome e Catalase Nitrate reductase Ammonium oxidase ... 

The element molybdenum (atomic weight 95.95) constitutes 0.08% of the weight of nitrate reductase. If the molecular weight of nitrate reductase is 240,000, what is its likely quaternary structure ... 

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. 

Chlorella vulgaris nitrate reductase structure, 3,1438 Chlorides... 

Mariotti, A., Mariotti, F., Champigny, M.L., Amarger, N. and Moyse, A. 1982 Nitrogen isotope fractionation associated with nitrate reductase activity and uptake of NO3by pearl millet. Plant Physiology 69 880-884. 

Nitrate reductase (respiratory) (QH2 nitrate reductase) Glutamate synthase Aerobic bacteria NO3- + QH, NOf + q S[Fe,S,r [FesS ] " Mo-cofactor +GO 24,55... 

Fig. 6. Comparison of VTMCD spectra for biological [Fe3S4] clusters. (A) D. gigas Fdll (20) (B) P. furiosus 3Fe Fd (42) (C) A. vinelandii Fdl (70) (D) T. thermophilus 7Fe Fd (70) (E) E. coli nitrate reductase (24) (F) E. coli fumarate reductase (53) (G) spinach glutEimate synthase (25) (H) beef heart aconitase (27). Spectra were recorded at temperatures between 1.5 and 70 K with an apphed magnetic field of 4.5 T (sdl trEmsitions increase in intensity with decreasing temperature). BEmds originating from minor heme contaminEmts Eire indicated by an asterisk.

Sulfate reducers can use a wide range of terminal electron acceptors, and sulfate can be replaced by nitrate as a respiratory substrate. Molybdenum-containing enzymes have been discovered in SRB (also see later discussion) and, in particular, D. desulfuricans, grown in the presence of nitrate, generates a complex enzymatic system containing the following molybdenum enzymes (a) aldehyde oxidoreduc-tase (AOR), which reduces adehydes to carboxylic acids (b) formate dehydrogenase (FDH), which oxidizes formate to CO2 and (c) nitrate reductase (the first isolated from a SRB), which completes the enzy-... 

The molyhdopterin cofactor, as found in different enzymes, may be present either as the nucleoside monophosphate or in the dinucleotide form. In some cases the molybdenum atom binds one single cofactor molecule, while in others, two pterin cofactors coordinate the metal. Molyhdopterin cytosine dinucleotide (MCD) is found in AORs from sulfate reducers, and molyhdopterin adenine dinucleotide and molyb-dopterin hypoxanthine dinucleotide were reported for other enzymes (205). The first structural evidence for binding of the dithiolene group of the pterin tricyclic system to molybdenum was shown for the AOR from Pyrococcus furiosus and D. gigas (199). In the latter, one molyb-dopterin cytosine dinucleotide (MCD) is used for molybdenum ligation. Two molecules of MGD are present in the formate dehydrogenase and nitrate reductase. 

The molybdenum cofactor was liberated from D. gigas AOR, and under appropriate conditions was transferred quantitatively to nitrate reductase in extracts of Neurospora crassa nit-1 mutant) to yield active nitrate reductase 217). On the basis of molybdenum content, the activity observed for reconstitution with molybdenum cofactor of D. gigas was lower (25%) than the values observed for the procedure using extractable molybdenum cofactor of XO, used as reference. This result can now be put in the context of the difference in pterin present (MPT-XO and MCD-AOR) 218). 

D. desulfuricans is able to grow on nitrate, inducing two enzymes that responsible for the steps of conversion of nitrate to nitrite (nitrate reductase-NAP), which is an iron-sulfur Mo-containing enzyme, and that for conversion of nitrite to ammonia (nitrite reduc-tase-NIR), which is a heme-containing enzyme. Nitrate reductase from D. desulfuricans is the only characterized enzyme isolated from a sulfate reducer that has this function. The enzyme is a monomer of 74 kDa and contains two MGD bound to a molybdenum and one [4Fe-4S] center (228, 229) in a single polypeptide chain of 753 amino acids. FXAFS data on the native nitrate reductase show that besides the two pterins coordinated to the molybdenum, there is a cysteine and a nonsulfur ligand, probably a Mo-OH (G. N. George, personal communication). 

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