Ferredoxin-NAD reductase

However, in contrast to the cyclic flow of electrons in purple bacteria, some electrons flow from the reaction center to an iron-sulfur protein, ferredoxin, which then passes electrons via ferredoxin NAD reductase to NAD+, producing NADH. The electrons taken from the reaction center to reduce NAD+ are replaced by the oxidation of H2S to elemental S, then to SOf, in the reaction that defines the green sulfur bacteria. This oxidation of H2S by bacteria is chemically analogous to the oxidation of H20 by oxygenic plants. 

This enzyme is homologous to the ferredoxin NAD reductase of green sulfur bacteria (Fig. 19-47b). 

Bes T, Gomez-Moreno C, Guisan JM et al. (1995) Selective enzymatic oxidations stabiUzation by multipoint covalent attachment of ferredoxin NAD-reductase an interesting cofactor recycling enzyme. J Mol Catal 98 161-169... 

The dioxygenase systems consist of a reductase and a terminal oxygenase many dioxygenases also contain a [2Fe-2S] ferredoxin. The reductase reacts with NAD(P)H it can be any of the following (20) ... 

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. 

The catalytic significance of this observation is not known since no deviation from a two-electron Nemst plot is observed with NADH as reductant and no kinetic studies have been done to compare the rate of the NAD -facilitated comproportionation reaction with the rate of catalytic turnover. No comparable studies on the effect of NADP on the oxidation-reduction potential of ferredoxin-NADP reductase have been, to our knowledge, published. Inasmuch as the physiological role for this enzyme is reduction of the pyridine nucleotide rather than its oxidation, the potential of the enzyme should be significantly lower than that of the pyridine nucleotide couple. Indeed, a value of —445 mV has been determined for this flavoenzyme with the driving force for its reduction being due to a decrease of 90 mV in the one-electron potential of the ferredoxin reductant. This increase... 

Ru(II)tris(bipyridine) [Ru(bpy)3 +] as a photosensitizer, triammonium ethylene-diaminetetraacetic acid [(NH4)3EDTA] as a sacrificial electron donor and the enzyme ferredoxin NADP+ reductase (FDR) [215, 216]. Oxidative electron-transfer quenching of the excited Ru(bpy)3 + yields the A,A -dimethyl-4,4 -bipyridinium radical cation (reduced methylviologen, MV+), which mediates the reduction of NADP+ in the presence of FDR as a biocatalyst (Figure 32A). The quantum efficiency for NADH production corresponds to = 1.9 x 10 . A related system that includes Zn(II)wc50-(A-tetramethylpyridinium)porphyrin (Zn-TMPyP +) as a photosensitizer, mercaptoethanol as a sacrificial donor and lipoamide dehydrogenase (LipDH) as a biocatalyst has been applied for the photochemical reduction of NAD+ to NADH (Figure 32B). 

The herbicidal effect of paraquat is attributable to the formation of superoxide anion (02 ). Superoxide anion is very toxic compound and is formed by the reaction of oxygen with paraquat radical (paraquat ). Plants, algae, and cyanobacteria have ferredoxin-NADP reductase to form NADPH for the reduction of carbon dioxide (see below). The chemolithoautotrophs also have NAD(P) (NAD and NADP) reductase to form NAD(P)H for the reduction of carbon dioxide. Paraquat [mid-point redox potential at pH 7.0 (Emj 0) = -0.43 V] radical is produced when paraquat is reduced by the catalysis of ferredoxin-NAD(P) reductase or NAD(P) reductase, which catalyzes the reduction of many compounds with of around -0.4 V. Although the aerobic organisms (and even many anaerobic organisms) have superoxide dismutase (SOD) which detoxifies superoxide anion in cooperation with catalase [ascorbate peroxidase in the case of plants (Asada, 1999)], the anion accumulates in the organisms when it is over-produced beyond the capacity of SOD. 

Electrochemical regeneration of NAD(P)H represents another interesting method 134 361. The system involves electron transfer from the electrode to the electron mediator such as methyl viologen or acetophenone etc., then to the NAD(P)+ (which is catalyzed by an electrocatalyst such as ferredoxin-NADP reductase or alcohol dehydrogenase, etc.) [34l Other methods involve the direct reduction of NAD on the electrode[35). Both one-enzyme systems and two-enzyme systems have been reported. 

The specific activities of ferredoxin-NAD oxidoreductase and butyiyl-CoA dehydrogenase (enoyl-CoA reductase. Scheme 3) increased 3-4 fold during growth on crotonate... 

Tejero J, Perez-Dorado 1, Maya C, Martinez-Julvez M, Sanz-Aparicio J, Gomez-Moreno C, Hermoso JA, Medina M (2005) C-terminal tyrosine of ferredoxin-NADP+ reductase in hydride transfer processes with NAD(P)+/H. Biochemistry 44 13477-13490... 

The regeneration of NAD(P)H with the participation of mediator-contacted enzymes ensures that NAD] )" " reduction proceeds selectively and that only enzymatically active NAD(P)H is produced. Many enzymes have been used in this context to provide the bio-electrocatalytic reduction of NAD(P)" ", for example, ferredoxin-NADP" " reductase (FNR) [245-249], lipoamide dehydrogenase [250-254], formate dehydrogenase... 

The pathway of the Clostridia for the formation of butyrate and acetate from glucose. 7 Embden-Meyerhof-Parnas pathway and hexose phosphotransferase, 2 pyruvate-ferredoxin oxidoreductase, 3a NAD(P)H-ferredoxin reductase, 3b ferredoxin-NAD(P) reductase,... 

Sequences of proteins containing Rieske-type clusters have been deduced from the complete operons of several dioxygenases these dioxygenases require electrons from NAD(P)H to convert aromatic compounds to cis-arene diols. The water-soluble dioxygenase systems consist of a reductase and a terminal dioxygenase many dioxygenases also contain a [2Fe-2S] ferredoxin (20). The terminal oxygenases contain a Rieske-type cluster and the ferredoxins may contain either a Rieske-type or a 4-cysteine coordinated [2Fe-2S] cluster. 

This iron-sulfur oxygenase [EC 1.14.12.11] catalyzes the reaction of molecular oxygen with toluene and NADH to produce (15 ,27 )-3-methylcyclohexa-3,5-diene-l,2-diol and NAD. This reductase is an iron-sulfur flavo-protein (FAD) that contains ferredoxin. Ethylbenzene, 4-xylene, and some halogenated toluenes can likewise undergo conversion to the corresponding cw-dihydro-diols. 

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