Enoate reductases catalyzed

Also, in case of enoate reductase-catalyzed reduction of conjugated C=C-double bonds promoted by ADHstable product (saturated carbonyl compound) [68]. 

Enoate reductase [153, 154], which occurs in strains of Clostridium or Proteus, and 2-oxo-acid reductase [155] from Proteus vulgaris or P. mirabilis catalyzes the stereospecific reduction of substrates performed directly by reduced methyl-viologen. No nicotinamide coenzyme is required. Methylviologen is regenerable electrochemically. Examples of the reduction of enoates, ketones, and 2-oxo acids are given in [155]. 

Reductions catalyzed by enoate reductase enantioselective hydrogenation of a, /6-unsaturated enoates and comparable compounds. 

To circumvent these issues, instead of wild-type whole cells, the use of cloned and overexpressed enoate reductases together with suitable redox enzymes for cofactor recycling - the so-called designer bugs - appears as an excellent ahemative to overcome the lack of selectivity observed when whole (fermenting) cell systems are applied, due to the existence of enzymes that can catalyze side reactions, and so on (Scheme 2.4) [18,19]. Thus, when enoate reductases are overexpressed, the enhancement of its concentration leads to higher selectivity and yields in the desired products. This area is clearly expanding nowadays, and therefore further innovations are ejqjected to appear. 

The very successful FDH regeneration system is also frequently evaluated to promote enoate reductase (ER)-catalyzed reductions of conjugated C=C double bonds [42]. With commercially available FDHs, however, a problem of overreduction is frequently encountered contaminating ADHs from the FDH-over-expressing strain also catalyze the NAD(P)H-dependent carbonyl reduction of the starting material and the product, which can lead to complex product mixtures. 

The so-called redox isomerizations represent a dass of internal redox reactions tvherein the overall redox state of the starting material remains unchanged. Again, this type of reaction is ideally suited to couple two oxidoreductase-catalyzed reactions with opposite cofactor demand. We [83] and others [84] have demonstrated the redox isomerization of allylic alcohols into the corresponding saturated ketones by coupling an ADH with an enoate reductase (ER) (Scheme 8.18). 

Stueckler, C., Reiter, T.C., Baudendistel, N., and Faber, K. (2010) Nicotinamide-independent asymmetric bioreduction of C=C bonds via disproportionation of enones catalyzed by enoate reductases. Tetrahedron, 66, 663-667. 

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