Nitrite reductase dissimilatory

With M. gryphiswaldense, Schuler and Bauerlein (1996) recorded an Fe uptake rate from Fe " citrate of 0.86 nmol min mg dry weight and suggested that the major portion of Fe is taken up in an energy-dependent process possibly by a reductive step (Schuler, 1999). Fukumori et al. (1997) proposed that the dissimilatory nitrite reductase of M. magnetotacticum may function as an Fe" oxidizing enzyme. Later, Fuko-mori (2000) suggested an Fe "quinate complex as the source of Fe which is subsequently reduced in the cell in a microaerobic environment at about neutral pH by the iron reductase NADH (an assimilatory enzyme). 

V. DISSIMILATORY NITRITE REDUCTASES, ENZYMES THAT GENERATE NITRIC OXIDE IN DENITRIFYING BACTERIA... 

Alefounder, P. R., and Ferguson, S. J. (1980). The location of dissimilatory nitrite reductase and the control of dissimilatory nitrate reductase by oxygen in Paracoccus denitri-ficans. Biochem.J. 192, 231-240. 

Kim, C.-H., and Hollocher, T. C. (1983). N tracer studies on the reduction of nitrite by the purified dissimilatory nitrite reductase of Pseudomonas aeruginosa.]. Biol. Chem. 258, 4861-4863. 

Urata, K., and Satoh, T. (1991). Enzyme localization and orientation of the active site of dissimilatory nitrite reductase from Bacillus firmus. Arch. Microbiol. 156, 24-27. 

Figure 16-6 Structures of isobacteriochlorin prosthetic groups. (A) Siroheme from nitrite and sulfite reductases (B) acrylochlorin heme from dissimilatory nitrite reductases of Pseudomonas and Paracoccus.

Two types of dissimilatory nitrite reductases catalyze step b of Eq. 18-30. Some bacteria use a copper-containing enzyme, which contains a type 1 (blue) copper bound to a (3 barrel domain of one subunit and a type 2 copper at the catalytic center. The type 1 copper is thought to receive electrons from the small copper-containing carrier pseudoazurin (Chapter... 

The dissimilatory nitrite reductase (cytochrome cdlt see below) catalyzes the nitrosation of several nucleophiles by nitrite.1531 This may occur through a heme-nitrosyl in which an NO+ group is present. Coordinated nitrite in simple metal complexes such as [Run(NH3)5(N02)]+... 

In addition, there have been several reports of reduced porphyrin or oxophlorin tt-cation radicals of Fe. Since it has been suggested that Fe isobacteriochlorin TT-cation radicals are viable species for at least two reaction states of the hemoprotein subunit of E. coli sulfite reductase and assimilatory nitrite reductases from several organisms, and at least one state of the heme d (chlorin) center of the dissimilatory nitrite reductases from several microorganisms, the investigation of the one-electron reduced states of these proposed intermediates has also been undertaken. 

Casciotti, K. L., and Ward, B. B. (2001). Dissimilatory nitrite reductase genes from autotrophic ammonia-oxidizing bacteria. Appl. Environ. Microbiol. 67, 2213—2221. 

In contrast, many gram-negative bacteria contain a nitrate reductase (EC 1.7.99.4 and/or 1.9.6.1) that also reduces nitrate to nitrite although under anaerobic conditions. The dissimilatory nitrite reduction leading to denitrification encompasses then the reduction of nitrite to nitric oxide by dissimilatory nitrite reductases (NiR, EC 1.7.2.1) that, in combination with nitric oxide reductases (NOR) and nitrous oxide reductases (N2OR), transform nitrite into nitrogen ... 

Hi) Coordination of nitrite and release of NO by the dissimilatory nitrite reductase (NiR) enzymes (either Fe- or Cu-based)11... 

The emerging picture of dissimilatory nitrite reductases as diheme proteins is upset by the P. denitrificans enzyme a nonheme, copper-containing protein of molecular weight 150,000 (4 3). It has been suggested that the strain P. denitrificans is more appropriately classified with the Alcali-genes (see work cited in reference 361), and, if so, we would be less surprised at finding a difference between its reductase and those of the other Pseudomonas strains. 

Bacterial assimilatory nitrate reductases have similar properties.In addition, many bacteria, including E. coli, are able to use nitrate ions as an oxidant for nitrate respiration under anaerobic conditions (Chapter 18). The dissimilatory nitrate reductases involved also contain molybdenum as well as Fe-S centers. The 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. Nitrate reduction to nitrite is also on the pathway of denitrification, which can lead to release of nitrogen as NO, N2O, and N2 by the action of dissimilatory nitrite reductases. These enzymes have been discussed in Chapters 16 and 18. 

Nitrite reduction to nitric oxide is catalyzed by dissimilatory nitrite reductase. The enzymes purified from Alcaligenes faecalis (Iwasaki and Matsub-ara, 1971), Pseudomonas aeruginosa (Walker and Nicholas, 1961), andMj-crococcus denitrificans (Newton, 1969) have been shown to contain c d-type cytochrome. The nitrite reductase from Achromobacter cycloclastes does not... 

Dissimilatory nitrite reductase of denitrifying bacteria is usually a soluble enzyme and it has been difficult to ascribe a phosphorylative function associated with the conversion of nitrite to nitric oxide. However, the demonstration by Wood (1978) that the terminal reductase in nitrite respiration is located in the periplasm implies that electrons generated in the cytoplasm must traverse the cytoplasmic membrane to the periplasmic nitrite reduction site. This location would require proton pumping, thus facilitating phosphorylation by the chemiosmotic mechanism. 

Dissimilatory nitrite reductases (NiR) play a pivotal role in the anaerobic respiration cascade of denitrifying bacteria, archaea and fungi by catalysing the first committed step of the pathway.The net reaction of NiR yields the conversion of nitrite (N02 ) into gaseous nitric oxide (NO) and water (H2O) (eqn (3.12) ref. 207) ... 

Abraham, Z. H. L., D. J. Lowe, and B. E. Smith. 1993. Purification and characterization of the dissimilatory nitrite reductase from Alcaligenes xylosoxidans subsp. xylosoxidans (NCIMB 11015). Evidence for the presence of both type-1 and type-2 copper centers. Biochem. J. 295 587-593. 

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