NADH-dependent -reductase

The kind of enantiomer [d-(-)- or l-(+)-] synthesized in the formation of the C4 intermediate varies. The acetoacetyl-CoA reductase (EC 1.1.1.36), which is NADPH-dependent, stereoselectively reduces acetoacetyl-CoA to d-(-)-3-hydroxybutyryl-CoA (R. eutropha [15]). The NADH-dependent reductase catalyzes the reduction of acetoacetyl-CoA to L-(+)-3-hydroxybutyryl-CoA. Afterwards two stereospecific crotonyl-CoA hydratases, l-(+)- and D-(-)-speci-fic, convert the L-(+)-3-hydroxybutyryl-CoA into the D-(-)-isomer (Rhodo-spirillum rubrum [16]). 

The NADPH-dependent reductase is active with C4 to C6 D-(-)-3-hy-droxyacyl-CoAs, it has no activity with L-(+)-substrates, and the reduction of acetoacetyl-CoA yields only D-(-)-3-hydroxybutyryl-CoA. The NADH-de-pendent reductase can use the L-(+)-enantiomers of these compounds and, in addition, C7, C8, and C10 L-(+)-3-hydroxyacyl-CoAs as substrates. From aceto-acetyl-CoA the NADH-dependent reductase produces only L-(+)-3-hydro-xybutyryl-CoA, but in the reverse direction it is active with both substrates [15]. 

The yeast-mediated enzymatic biodegradation of azo dyes can be accomplished either by reductive reactions or by oxidative reactions. In general, reductive reactions led to cleavage of azo dyes into aromatic amines, which are further mineralized by yeasts. Enzymes putatively involved in this process are NADH-dependent reductases [24] and an azoreductase [16], which is dependent on the extracellular activity of a component of the plasma membrane redox system, identified as a ferric reductase [19]. Recently, significant increase in the activities of NADH-dependent reductase and azoreductase was observed in the cells of Trichosporon beigelii obtained at the end of the decolorization process [25]. 

Kometani et al. [71] reported that baker s yeast catalyzed the asymmetric reduction of acetol to (i )-1,2-propanediol with ethanol as the energy source. The enzyme involved in the reaction was an NADH-dependent reductase, and NADH required for the reduction was supplied by ethanol oxidizing enzyme(s) in the yeast. When washed cells of baker s yeast were incubated with 10 mg ml of acetol in an ethanol solution with aeration, (k)-1,2-propanediol was formed almost stoichiometrically with an optical purity of 98.2% e. e. 

The NADH-dependent reductase, which contains a 2Fe 2S cluster and FAD as cofactors, converts the oxidized hydroxylase binuclear cluster to a diferrous state after each catalytic cycle. It should be emphasized that the reductase does not participate directly in the hydroxylation reaction its sole function is to regenerate the reduced enzyme in a separate reaction (Fox et al., 1988). The latter reacdon is reminiscent of the NADH-linked reducdon of inactive diferric RNRB2 (see Section III,B). 

NADH-dependent reductase, thus allowing the biopterin cofactor to function catalytically (72JBC(247)6082). That the conversion of phenylalanine to tyrosine involves an arene oxide intermediate is suggested by the observation of the so-called NIH shift phenomenon (i.e. migration and retention of the para substituents such as deuterium, tritium, methyl and bromine when these para-substituted phenylalanines are enzymatically hydroxylated) <66BBR(24)720, 67MI11000). 

The mechanistic aspect of the fungal reduction of metal ions led by colloidal suspension is still an open question. However, in the fungal case, this process occurs probably either by reductase action or by electron shuttle quinines, or both. To elucidate the mechanism of nanoparticles formation, a novel fungal/enzyme-based in vitro approach was for the first time explained by Mukherjee et al. (2002). They successfully used species-specific NADH-dependent reductase, released by the F. oxysporum, to carry out the reduction of AuClJ ions to gold nanoparticles. Duran et al. (2005) later reported that the reduction of the metal ions occnrs by a nitrate-dependent reductase and a shuttle quinone extracellular process. The same... 

The keto-sugar nucleotide dTDP-L-rhamnose is synthesized from dTDP-4-keto-6-deoxy-D-glucose by dTDP-i-rhamnose synthase [104, 105). The enzyme consists of two components, a cofactor independent epimerase and an NADH-dependent reductase. The epimerase component is inactive without the reductase component. The mechanism involves epimerization of two stereocenters flanking a carbonyl group, via sequential deprotonation/reprotonation, with two enol intermediates. Complete solvent isotope incorporation into both epimerized stereocenters was observed, and primary substrate-derived KIEs have been determined [104],... 

Both the biosynthetic and degradative fatty acid cycles contain two oxidoreductases each. In the biosynthetic pathway, the /3-ketoacyl-ACP formed by the KAS enzymes is reduced by an NADPH-dependent reductase, encoded by the fabG gene in E. coli. Following a dehydration step, the resulting enoyl-ACP is reduced by an enoyl-ACP reductase, encoded by xS fahlin E. coli. FabI is an NADH-dependent reductase, and both FabI and FabG are members of the SDR superfamily. Not all bacteria utilize FabI as their enoyl-ACP reductase, and currently, three other enzymes that include FabV, FabL, and FabK are known. Both FabV and FabL are also members of the SDR family however, the flavin-dependent enoyl-ACP reductase FabK is not. 

As will be shown in Sections 5 and 6 methylviologen can be reduced at the cathode of an electrochemical cell to the mono cation radical MV which transfers electrons by the action of an enzyme type which we call AMAPOR for artificial mediator accepting pyridine nucleotide pxidoreductase. Finally the NADH is used for reducing the substrate by the catalytic action of an NADH dependent reductase. 

Currently, the mechanism of biological nanoparticle synthesis is not fully understood. For gold nanoparticles synthesized extracellularly by the fungus F. oxyspo-rum, it was reported that the reduction occurs due to NADH-dependent reductase released into the solution [16]. With neem leaf broth, it was reported that terpenoids are believed to be the surface-active molecules stabilizing the nanoparticles, and reaction of the metal ions is possibly facilitated by reducing sugars or terpenoids... 

In Rhodopsuedomonas rubrum, the pathway differs after the second step where the acetoacetyl-CoA formed by p-ketothiolase is reduced by a NADH-dependent reductase to L-(+)-3-hydroxybutyryl-CoA which is then converted to D-( )-3-hydroxybutyryl-CoA by two enoyl-CoA hydratases. 

Zhang, Y, Gao, F Zhang, S.P., Su, Z.G., Ma, G.H., and Wang, P. (2011) Highly efficient synthesis of chiral alcohols with a novel NADH-dependent reductase from Streptomyces codicolor. Biores. Technol., 102, 1837-1843. 

An NADH-dependent reductase (ScCR) was identified by genome mining studies of Streptomyces coelicolor. This dehydrogenase showed broad tolerance to pro-chiral ketones including aryl ketones, a- and 3-ketoesters and had particularly high activity and excellent enantioselectivity (>99% ee) for the last substrate type For example the enzyme reduced ethyl 4-chloro-3-oxobutanoate (CORE)... 

---