Nitrite reductase bacteria

Cytochrome c nitrite reductase (bacteria) Reduces HA and NH2OCH3 to ammonia (NH3) 10, 23... 

In 1973, the first naturally occurring isobacteriochlorin, iron-containing siroheme, was isolated1 from a sulfite reductase of Escherichia coli. Later it was also discovered in sulfite and nitrite reductases of numerous bacteria and plants.2 Iron-free sirohydrochlorins (also called factor II) were discovered in vitamin B12 producing bacteria.3-4 Together with factor III. a sirohydrochlorin methylated in the 20-position, the reduced forms of factor II and factor III were identified as biosynthetic intermediates in the biosynthesis of vitamin B12.5... 

While nitrite reductases in many bacteria are haem proteins, some are copper containing homotrimers, which bind three Type I and three Type II copper centres. The Type I copper... 

Nitrite reductases (NiRs)—enzymes found in several strains of denitrifying bacteria— catalyze the one-electron reduction of nitrite anion to nitric oxide (Equation 1). - In addition to the importance of this process in the global nitrogen cycle (Figure 1), further incentive for the study of the denitrification process is provided by its environmental impact, ranging from the production of NO as a pollutant and NjO as a potent greenhouse gas, to lake eutrophication due to farm runoff that contains high concentrations of nitrates and nitrites. 

Blom was the first to demonstrate, in 1928, the formation of HA by an unknown mixture of bacteria which utilized nitrate as their sole nitrogen source to produce ammonia , an observation substantiated by Lindsey and Rhines who generalized this reaction to a diverse set of microorganisms capable of producing NH3 by reduction of both nitrites and nitrates. The mechanism of the 6-electron reduction of nitrite to ammonia (i.e. conversion of the [N + 02] species to by bacterial cytochrome c nitrite reductase... 

Nitrite reductase Denitrification Denitrifying bacteria Liu etal. (1986)... 

O-exchange studies of Ye et al. (1991) support, we believe, the catalysis by nitrite reductase of redox reversibility between nitrite and NO as depicted in the first line of Eq. (3). They observed by analyzing the 0 content of product N2O that all eight strains of denitrifying bacteria studied could catalyze the exchange of 0 between water and nitrite or NO by way of an electrophilic (nitrosyl donor) species of NO. The rates and extent of these exchange reactions depended on whether the bacterium made use of a heme- or Cu-type nitrite reductase. Contrary to the conclusions of Ye et al. (1991), we do not believe that this study otherwise informs about the pathway of denitrification or whether NO is an intermediate. 

Although the nitrite reductases of denitrifying bacteria seem to be NO-pro-ducing reductases in vitro, we cannot so easily say that they similarly are NO-producing in vivo. It is not so rare for an enzyme to catalyze more than one reaction or be served by more than one substrate, but it is virtually without precedence for an enzyme to change its chemistry with the same substrate between in vivo and in vitro situations. The reduction of nitrite in vivo has been probed by several means which target the activity of either nitrite or nitric oxide reductase. 

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

Denitrifying bacteria produce one or the other of two usually soluble but very dissimilar nitrite reductases, heme- and Cu-containing types (Brittain et al., 1992 Coyne et al., 1989), both of which are found in the periplasmic space of gram-negative bacteria (Coyne et al., 1990). 

Although the Cu-type family of nitrite reductase is comprised of soluble enzyme and localized in the periplasmic space in gram-negative bacteria, it has proved to be a membrane-bound enzyme in denitrifying Bacillus, which is gram positive and lacks an outer membrane and periplasmic space (Denariaz et ai, 1991 Urata and Satoh, 1991 Ho etal., 1993). 

It was long believed that bacteria were unique in their ability to denitrify. However, Shoun and Tanimoto (1991) and Shoun et al., (1989) demonstrated that the fungus, Fusarium oxysporum, could be induced to synthesize an enzyme system capable of the anaerobic reduction of nitrite to N2O. Induction occurred under conditions of low oxygen concentrations in the presence of nitrate or nitrite. One and pethaps the only component of this nitrite reductase system is a unique, soluble cytochrome P-450 (P-450dNIR), which is more similar in its cDNA-inferred amino acid sequence to soluble, bacterial P-450 enzymes (espe-... 

Calmels, S., Ohshima, H., and Bartsch, H. (1988). Nitrosamine formation by denitrifying and non-denitryfying bacteria Implications of nitrite reductase and nitrate reductase in nitrosation catalysis. . Gen. Microbiol. 134, 221-226. 

Coyne, M. S., Arunakumari, A., Averill, B. A., and Tiedje, J. M. (1989). Immunological identification and distribution of dissimilatory heme cd, and nonheme copper nitrite reductases in denitrifying bacteria. Appl. Environ. Microbiol. 55, 2924-2931. 

Heme d is a chlorin,85 as is acrylochlorin heme from certain bacterial nitrite reductases (Fig. 16-6).86 87 Siroheme (Fig. 16-6), which is found in both nitrite and sulfite reductases of bacteria (Chapter 24) 38/89 is an isobacteriochlorin in which both the A and B rings are reduced. It apparently occurs as an amide siroamide (Fig. 16-6) in Desulfovibrio.90 Heme of nitrite reductases of denitrifying bacteria is a dioxo-bacteriochlorin derivative (Fig. 16-6).91 92... 

Iron-sulfur clusters are found in flavoproteins such as NADH dehydrogenase (Chapter 18) and trimethylamine dehydrogenase (Fig. 15-9) and in the siroheme-containing sulfite reductases and nitrite reductases.312 These two reductases are found both in bacteria and in green plants. 

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