Nitrate enzymatic reduction

ISO. 2000. Determination of nitrate and nitrite contents—Method by enzymatic reduction and molecular absorption spectrometry after Griess reaction. Ref. No. ISP/TC 34/SC5 N546. Delft, The Netherlands International Organization for Standardization. 

Bacteria have been Implicated in the formation of N-nitroso compounds under a wide variety of conditions representing both vitro and vivo situations Mechanisms of participation and/or catalysis Include a) decrease of the pH of the system, b) reduction of nitrate to nitrite, c) adsorption of amine onto the cell surface or cytoplasmic membrane, d) actual enzymatic formation. The literature of the field will be reviewed and experimental evidence which tests the above mechanisms will be presented ... 

Investigation of the mechanism of nitrate reduction by Desulfovibrio desulfuricans nitrate reductase at various levels of theory has confirmed the utility of the orbital-free embedding method in the description of enzymatic processes.379... 

Biocatalytic synthetic reactions also include carbon dioxide fixation with the production of methanol in artificial multi-enzyme systems [188]. Formate dehydrogenase (FDH, EC 1.2.1.2) can catalyze the reduction of carbon dioxide to formate, and methanol dehydrogenase (MDH, EC 1.1.99.8) can catalyze the reduction of formate to methanol. Both of these enzymes require NAD+-NADE1 cofactor, and in the presence of the reduced dimethyl viologen mediator (MV+), they can drive a sequence of enzymatic reactions. The cascade of biocatalytic reactions results in the reduction of CO2 to formate catalyzed by FDEI followed by the reduction of formate to methanol catalyzed by MDH. A more complex system composed of immobilized cells of Parococcus denitrificans has been demonstrated for the reduction of nitrate and nitrite [189]. 

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). 

Studies of the antimicrobial and therapeutic properties of silver and its derivatives have yielded an extensive scientific literature, ranging from clinically- to biochemically-based papers. The latter area includes studies in enzymatic and other macromolecular interactions to silver resistance encompassing plasmid-mediated patterns. The reduction to one silver compound (AgSD) in the current British National Formulary and to two compounds (AgSD and silver nitrate ophthalmic solution) in USP XXII may not be a true reflection of the use of silver in health care today. Silver compounds also find use in non-clinical situations, for example, as water disinfectants and, not considered in this review, as silver staining techniques for microscopy. 

Reduction of membrane-impermeable oxidants by intact cells of T. weissflogii occurs without the addition of extracellular reductants, by a process mediated by i transplasmamembrane redox system (Fig. 3b). In the light and in the dark, enzymatic processes actively reduce Cu and Fe complexes with reduction potentials between — 100 and +100 mV. The rate of reductant consumption in iliis process [a few fcmtomoles of Cu(II) reduced per cell per hour] can be as high as 10% of the rates of carbon fixation and nitrate reduction. In other words, i eduction of extracellular solutes by cells potentially diverts a significant portion <>l photochemically genera led electrons out of the cell. 

In the processes of the enzymatic oxidation of nitrite, the reduction by nitrite of cytochrome c-550 hardly occurs because EmJ,0 (midpoint redox potential) of nitrite/ nitrate system (+0.40 V) is higher than that of cytochrome c-550 (+0.28 V). The reduction step of molecular oxygen catalyzed by cytochrome c oxidase proceeds rapidly, because EmJ,0 of H20/02 system is +0.82 V and is very much higher than that of cytochrome c-550. Therefore, in the bacterium, the electron flow from nitrite... 

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