Ferredoxin-nitrite reductase

This redox protein participates in several enzyme-catalyzed reactions, including glutamate synthase (ferredoxin) [EC 1.4.7.1] ferredoxin-nitrite reductase [EC... 

Nitrite reductase (NAD(P)H) [EC 1.6.6.4] catalyzes the reaction of three NAD(P)H with nitrite to yield three NAD(P)+, NH4OH, and water. Cofactors for this enzyme include FAD, non-heme iron, and siroheme. (2) Nitrite reductase (cytochrome) [EC 1.7.2.1] is a copper-depen-dent system that catalyzes the reaction of nitric oxide with two ferricytochrome c and water to produce nitrite and two ferrocytochrome c. (3) Ferredoxin-nitrite reductase [EC 1.7.7.1], a heme- and iron-dependent enzyme, catalyzes the reaction of ammonia with three oxidized ferredoxin to produce nitrite and three reduced ferredoxin. (4) Nitrite reductase [EC 1.7.99.3] is a copper- and FAD-dependent enzyme that catalyzes the reaction of two nitric oxide with an acceptor substrate and two water to produce two nitrite and the reduced acceptor. 

Ogawa, M. Ida, S. (1987) Biosynthesis of ferredoxin nitrite reductase in rice seedlings. Plant and Cell Physiology 28, 1501-8. 

Krueger, R.J. and L.M. Siegel (1982). Spinach siroheme enzymes Isolation and characterization of ferredoxin-sulfite reductase and comparison of properties with ferredoxin-nitrite reductase. Biochemistry 21, 2892-2904. 

Lancaster, J.R., J.M. Vega, H. Kamin, N.R. Orme-Johnson, W.H. Orme-Johnson, R.J. Krueger, and L.M. Siegel (1979). Identification of the hon-sulfur center of spinach ferredoxin-nitrite reductase as a tetranuclear center, and preliminary EPR studies of mechanism. J. Biol. Chem. 254, 1268-1272. 

Mikami, B. and S. Ida (1989). Spinach ferredoxin-nitrite reductase Characterization of catalytic activity and interaction of the enzyme with substrates. J. Biochem. 105, 47-50. 

Wilkerson, J.O., P.A. Janick, and L.M. Siegel (1983). Electron paramagnetic resonance and optical spectroscopic evidence for interaction between siroheme and tetranuclear iron-sulfur center prosthetic groups in spinach ferredoxin-nitrite reductase. Biochemistry 22, 5048-5054. 

The rate of reduction of cytochrome c by the cobalt-substituted analogue of rubredoxin is a factor of 2.25 lower than the rate with rubredoxin itself. Both proteins mediate the reduction of cytochrome c in the presence of NADH and the decrease in the rate is attributed to the decreased efficiency in oxidation of cobalt(ii) compared with iron(ii). Reduction of cytochrome c by NADPH is catalysed by an adrenodoxin reductase-adrenodoxin complex in which the rate-determining step is electron transfer from the flavin (FAD) of the reductase to the FeaS2 centre of adrenodoxin. The pH dependence of the rate shows a pATa of 6.75, with the high-pH form 27.5 times more reactive than the low-pH form. Both NADPH reduction of the complex and cytochrome c oxidation of the complex were faster than the catalytic rate. Catalytic roles of four iron-sulphur centres in trimethylene dihydrogenase and ferredoxin nitrite reductase have also been examined. Synthetic analogues of four iron ferredoxins have also attracted much attention. - ... 

Fe Cytochrome oxidase reduction of oxygen to water Cytochrome P-450 0-insertion from O2, and detoxification Cytochromes b and c electron transport in respiration and photosynthesis Cytochrome f photosynthetic electron transport Ferredoxin electron transport in photosynthesis and nitrogen fixation Iron-sulfur proteins electron transport in respiration and photosynthesis Nitrate and nitrite reductases reduction to ammonium... 

Spinach nitrite reductase,313 which is considered further in Chapter 24, utilizes reduced ferredoxin to carry out a six-electron reduction of N02 to NH3 or of SO-2 to S2. The 61-kDa monomeric enzyme contains one siroheme and one Fe4S4 cluster. A sulfite reductase from E. coli utilizes NADPH as the reductant. It is a large (38a4 oligomer.312 The 66-kDa a chains contain bound flavin... 

Assimilatory nitrite reductases of plants, fungi, and bacteria carry out the six-electron reduction of nitrite to ammonium ions (Eq. 24-13) using electron donors such as reduced ferredoxins or NADPH. 

Fig. 1. The nitrate assimilation pathway in higher plants. The pathway of nitrate assimilation in the tobacco leaf is illustrated. In some other species an additional cytosolic GS is found in the leaf. The pathway in plant roots is more poorly documented and more variable GS in roots is mostly cytosolic, and some enzymes such as GOGAT are found as isoforms utilising alternate reducing substrates. T, expected nitrate carrier NR, nitrate reductase NiR, nitrite reductase GS, glutamine synthetase GOGAT, glutamate synthase Fd, ferredoxin Gin, glutamine Glu, glutamate.

In a plant, nitrite reductase catalyses reduction of its substrate to ammonia, which is subsequently incorporated into cell material. This type of nitrite reductase is classified as an assimilatory enzyme. The plant enzyme is found in the chloroplasts and acquires reductant from ferredoxin which is in turn reduced by the action of the photosystems that derive electrons... 

The laser photolysis results on the ET behavior of these mutants have been confirmed by steady-state kinetic measurements [58, 59]. Interestingly, the latter experiments have shown that nonconservative mutations at F65 and E94 not only severely inhibit reactivity with FNR, but also with two other ferredoxin-dependent enzymes, nitrite reductase and nitrate reductase [58]. Apparently, similar structural constraints in their interactions with Fd are also operative in these other enzymes. 

A nitrite reductase in H. marismortui[ A5] causes the disappearance of nitrite in the presence of dithionite with either methylviologen or the organism s ferredoxin as the electron mediators. The product of reduction is presumed to be nitric oxide. 

In all photoautotrophs, reduction of NOj" to NH4 is achieved in two distinct enzymatic steps (Campbell, 2001). First, assimilatory nitrate reductase (NR) catalyzes the two electron reduction from NOj" to NO2. NR is a large soluble cytoplasmic enzyme with FAD (flavin adinine dinucleotide), an iron-containing cytochrome and molybdopterin prosthetic groups, and requires NADH and/or NADPH as an electron donor (Guerrero et al, 1981). Functional NR is in the form of a homodimer and therefore requires two atoms of iron per enzyme. Following transport into the chloroplast, NO2 undergoes a 6 e reduction to NH4 via assimilatory nitrite reductase (NiR). NiR, a soluble chloroplastic enzyme, contains five iron atoms per active enzyme molecule, and requires photosynthetically reduced ferredoxin as an electron donor (Guerrero et al., 1981). 

Top, right P. furiosus ferredoxin. Bottom, left 4-a-helix-bnndle synthetic protein. Bottom right A xylosoxidans Cu-nitrite reductase. 

Robust voltammetry and in situ STM to molecular resolution have been achieved when the Au(lll)-electrode surfaces are modified by linker molecules, Fig. 8-10, prior to protein adsorption. Comprehensive voltammetric data are available for horse heart cyt and P. aeruginosa The latter protein, which we address in the next Section, has in a sense emerged as a paradigm for nanoscale bioelectrochemistry. We address first briefly two other proteins, viz. the electron transfer iron-sulfur protein Pyrococcus furiosus ferredoxin and the redox metalloenz5mie Achromobacter xylosoxidans copper nitrite reductase. 

Ferredoxin is used by nitrogenase reductase (component II), an enzyme of nitrogen fixation, and also by nitrite reductase, which catalyzes reduction of nitrite to ammonia... 

The last three steps in the reduction of nitrate to ammonia are carried out by an enzyme called nitrite reductase. It contains one Fe2S2 center and one molecule of siroheme, a partially reduced iron porphyrin. The electron donor for each step is ferredoxin. 

See also The Nitrogen Cycle, Nitrogen Fixation, Utilization of Ammonia, Dimethylsulfoxide Reductase, Nitrite Reductase, Siroheme, Ferredoxin, Figure 20.2... 

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