Enzyme-catalyzed reductions

Enzyme catalyzed reductions of carbonyl groups are more often than not com pletely stereoselective Pyruvic acid for example is converted exclusively to (5) (+) lactic acid by the lactate dehydrogenase NADH system (Section 15 11) The enantiomer... 

Nitrogen fixation is any process in which N2 in the atmosphere reacts to form any nitrogen compound. Biological nitrogen fixation is the enzyme-catalyzed reduction of N2 to NH3, NH4, or any organic nitrogen compound. 

Fisher, J. Ramakrishnan, K. Becvar, J. E. Direct enzyme-catalyzed reduction of anthra-cyclines by reduced nicotinamide adenine dinucleotide. Biochemistry 1983, 22, 1347-1355. 

The asymmetric reduction of prochiral functional groups is an extremely useful transformation in organic synthesis. There is an important difference between isolated enzyme-catalyzed reduction reactions and whole cell-catalyzed transformations in terms of the recycling of the essential nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] cofactor. For isolated enzyme-catalyzed reductions, a cofactor recycling system must be introduced to allow the addition of only a catalytic amount (5% mol) of NAD(P)H. For whole cell-catalyzed reductions, cofactor recycling is automatically achieved by the cell, and the addition of a cofactor to the reaction system is normally not required. 

Recently a new hybrid power source has been reported that couples oxidation at a dye-photosensitized nanocrystalline semiconducting SnOz photoanode with the enzyme-catalyzed reduction of O2. Although miniaturization has not yet been reported for this new hybrid, the developments already achieved to miniaturize biofuel cells coupled to those being developed for charge-insertion oxides should be technically transferable to this system. 

The enzymatic reduction of T-configured alkenones represents a valuable alternative to the enzyme-catalyzed reduction of the corresponding alkynone with subsequent partial reduction of the C-C triple bond. Nevertheless, since in our results the Z-configured vinylic alcohols are not accessible in enantiopure form by enzyme-catalyzed reduction of the olefinic ketones, for this class of compounds the two-step process via the propargylic alcohols is a highly valuable new strategy. 

Stromal isozymes of the glycolytic enzymes catalyze reduction of 3-phosphoglycerate to glyceraldehyde 3-phosphate each molecule reduced requires one ATP and one NADPH. 

Table 8. Preparation of chiral alcohols by enzyme-catalyzed reduction of the corresponding ketones with ADH from Lactobacillus kefir. The production of phenylethanol with formate and formate dehydrogenase (FDH) for coenzyme regeneration was carried out continuously in an enzyme-membrane-reactor...

Synthetic statins are important lipid regulating drugs for the treatment of atherosclerosis and other diseases related to hyperlipidaemia, especially coronary heart disease. As the pharmacophore, all synthetic statins contain a saturated or partially unsaturated syn-3,5-dihydroxy C7-carboxylate. An important building block for the synthesis of the side chain is represented by 4-chloro-3-hydroxybutanoate esters (CHBE). Both enantiomers can be obtained by enzyme-catalyzed reduction of the (1-keto ester. The group of Kataoka and Shimizu found that an aldehyde reductase of Sporobolomyces salmonicolor [161] and a carbonyl reductase of Candida... 

The HLADH-catalyzed reduction of ( )-(97) is of interest since the alcohol product (98) is the thermodynamically less-preferred exo epimer. This emphasizes the fact that the geometry of an initial, kineti-cally controlled, product of an enzyme-catalyzed reduction reflects only the direction of attack of the hydride equivalent that is imposed by the orientation of substrate binding in the ES-complex. In this case, the reduction occurs on the re face of (15 )-(97), in accord with the predictions of the active site... 

This enzyme catalyzes reduction of CO2 to formyl-MF (Reaction 48) during methanogenesis from CO2, and the oxidation of formyl-MF (the reverse of Reaction 48) during methylotrophic methanogenesis [184] ... 

Interestingly, our previously described studies concerning the in vitro biotransformation of aryl azides in murine microsomes [93] generally parallel the above results observed for the chemical reduction of azides by thiols, with electron-deficient aryl azides also undergoing metabolic reduction much more rapidly than their electron-rich counterparts or alkyl azides. These similarities have led us to speculate that a possible mechanism for the enzyme-catalyzed reduction of aryl azides may entail analogous initial attack by a sulphydryl group at the active site of the appropriate enzyme, although this hypothesis remains to be confirmed. 

Partly purified enzyme catalyzes reduction of NAD with xylitol or D-glucitol.268... 

FIGURE 17.11 Enzyme-catalyzed reduction of pyruvate to (S)-(+)-lactate. A preferred orientation of binding of pyruvate to the enzyme, coupled with a prescribed location of the reducing agent, the coenzyme NADH, leads to hydrogen transfer exclusively to a single face of the carbonyl group. 

Nitrosamines are formed whenever nitrosating agents come in contact with secondary amines. Indeed, more nitrosamines are probably synthesized within our body than enter it by environmental contamination. Enzyme-catalyzed reduction of nitrate (NOs ) produces nitrite (N02 ), which combines with amines present in the body to form A-nitroso amines. 

The enzymic-catalyzed reduction of cytochrome cox using the xanthine - xanthine oxidase reaction led to the assumption that Oi- was the active reducing agent (133). Myoglobin and carboanhydrase were able... 

Racemic mixtures of secondary alcohols can be resolved completely by enantiospe-cific enzyme-catalyzed oxidation resulting in one enantiomer of the alcohol and the ketone followed by asymmetric enzyme-catalyzed reduction of the ketone (Fig. 16.2-51). For oxidation and reduction, two separate microorganisms1217-2191 or two different enzymes in a single microorganism1220-2221 may be used. 

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