Nitrate reductase cytochrome

Figure 21. (A) The assembly of an integrated nitrate sensor electrode by the cross-linking of a microperoxidase-11-nitrate reductase (cytochrome-dependent, EC 1.9.6.1) affinity complex on an Au electrode. (B) Cyclic voltammograms of the integrated MP-ll-NR monolayer-modified Au electrode (roughness factor ca. 15). (a) 0.1 M phosphate buffer, pH 7.0 (b) in the presence of KNO3, 20 mM. Potential scan rate, 5 mV s . Inset electrocatalytic cathodic currents [E = —0.6 V vs. SCE) transduced by the modified electrode at different concentrations of KNO3. Measurements were performed under argon.

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. 

Microperoxidase-11, MP-11, is a heme-undecapeptide that is prepared by the digestion of cytochrome c and it includes the active surrounding of cytochrome MP-11 was immobilized on electrode surface s and its electrochemistry was characterized. The MP-11-modified electrodes were reported to act as effective electron mediator interfaces for the reduction of cytochrome c, hemoglobin, myoglobin and nitrate reductase (cytochrome c-dependent). The MP-11-mediated activation of nitrate reductase, NR, was employed to assemble an integrated MP-11/NR electrode for the bioelectrocatalyzed reduction of nitrate (NO3 ) to nitrite (NO2). An affinity complex between a MP-11-functionalized electrode and NR (/Q = 3.7x10 M ) was crosslinked with glutaric dialdehyde to yield the electrically contacted electrode for the bioelectrocatalyzed reduction of nitrate to nitrite. In this system the reduced MP-11 mediates ET to NR and activates the enzyme towards the reduction of NO3. 

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

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). 

Other examples using pulse radiolysis include (a) studies on cytochrome c-di nitrate reductase from Thio-sphaera pantotropha to provide evidence for a fast intramolecular electron transfer from c-heme to rate constant for the reaction of... 

CYTOCHROME cj HYDROGENASE CYTOCHROME c PEROXIDASE CYTOCHROME P-450 REDUCTASE MIXED-EUNCTION OXIDASE NADH-CYTOCHROME bs REDUCTASE NADH DEHYDROGENASE NITRATE REDUCTASE... 

NADH PEROXIDASE NITRATE REDUCTASE NADH-CYTOCHROME bj REDUCTASE NADH DEHYDROGENASE NADH DEHYDROGENASE (Other Than Complex I)... 

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. 

Generally, the assimilatory nitrate and nitrite reductases are soluble enzymes that utilize reduced pyridine nucleotides or reduced ferrodoxin. In contrast, the dissimilatory nitrate reductases are membrane-bound terminal electron acceptors that are tightly linked to cytochrome by pigments. Such complexes allow one or more sites of energy conservation (ATP generation) coupled with electron transport. 

The spectrum of reduced cytochrome d in E. coli membranes is affected by added nitrate. The new spectrum formed may be that of a nitrosyl complex. Similar but faster changes were brought about by nitrite, trioxodinitrate or NO.723 The nitrate may be reduced to nitrite by a nitrate reductase in a slow step, followed by further reduction by reduced d. These nitrate-induced spectral changes in cytochrome d had been attributed previously to Ag+ added as silver nitrate. 

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... 

Thus for dehydrogenase partial activities of NR, the 28kDa FAD domain alone is a NADH ferricyanide reductase (NADH FR) and the FAD domain linked to the haem domain (40kDa) is a NA DH cytochrome c reductase (NADH CR) as well as a NADH dichloro-phenolindophenol reductase (NADH.DR). As for the nitrate-reducing activities, the methylviologen nitrate reductase (MV NR) and the reduced flavin nitrate reductase (FMN NR) activities involve the MoCo domain (75 kDa) linked to the haem domain, whereas reduced brom-... 

Brown, J., Small, I.S. Wray, J.L. (1981). Age-dependent conversion of nitrate reductase to cytochrome c reductase species in barley leaf extracts. Phytochemistry 20, 389-98. 

Hyde, G.E. Campbell, W.H. (1990). High-level expression in Escherichia coli of the catalytically active flavin domain of corn leaf NADH-nitrate, reductase and its comparison to human NADH-cytochrome b5 reductase. Biochemical and Biophysical Research Communications 168, 1285-91. 

LS, K.H.D. Lederer, F. (1983). On the presence of a heme-binding domain homologous to cytochrome b5 in Neurospora crassa assimilatory nitrate reductase. The EMBO Journal 2, 1909-14. 

Nitrate reductase (assimilatory) Plants a2 (MPT)Mo(0)2tl Cysteine 2 Cytochrome b, 105,106... 

The enzymatic mechanisms of nitrate bioactivation have long been the subject of debate. The glutathione-S-transferase and cytochrome P-450 systems were thought to be involved [8], while recently a nitrate reductase that specifically catalyzes the formation of 1,2-glyceryl dinitrate from glyceryl trinitrate was purified and identified as a mitochondrial aldehyde dehydrogenase [46]. Interestingly, this... 

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 ... 

A cycle for substrate reduction can be devised by beginning at the reduced Mo(IV) state and reversing the direction of OAT and CEPT steps, as illustrated for the nitrate reductase reaction in Fig. 9(b). Electrons are provided to reduce Mo(VI) to Mo(IV) via cytochrome b and FAD. 

Campbell, W. H., 1992, Expression in Escherichia coli of cytochrome c reductase activity from a maize NADH nitrate reductase complementary DNA, Plant Physiol. 99 693fi... 

Lu, G., Lindqvist, Y., Schneider, G., Dwivedi, U., and Campbell, W. H., 1995, Structural studies on com nitrate reductase refined structure of the cytochrome b reductase fragment at 2.5 A, its ADP complex and an active-site mutant and modeling of the cytochrome b domain, J. Mol. Biol. 248 9319948. 

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. 

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