Glucose dehydrogenase , NADH regeneration

Figure 9. Preparation of L- and D-lactaldehyde and L- and D-2-hydroxybutyraldehyde. HLADH, horse liver alcohol dehydrogenase (NADH was regenerated by glucose/glucose dehydrogenase).

The most convenient and useful enzymatic methods for the regeneration of NAD(P)H are formate/formate dehydrogenase for NADH [210, 211], iso-propanol/TBADH for NADPH [57], isopropanol/ADH (Pseudomonas sp.) for NADH [61, 212] and glucose/glucose dehydrogenase (Bacillus sp.) for NADH and NADPH [213],... 

Hydrogen peroxide is not merely dismutated by catalase, but used as substrate in a second enzyme cascade reaction producing propylene oxide [123 1251. In an alternative process 1261 the reduction step was performed enzymatically using aldose reductase and formate dehydrogenase for NADH regeneration. Thus, essentially glucose free D-fructose was obtained. 

Continuous enzymatic production of xylitol with simultaneous coenzyme regeneration in a charged membrane reactor was studied (210). An NADH dependent xylose reductase from C. tenuis catalyzed the reduction of xylose. This was coupled to enzymatic oxidation of glucose by glucose dehydrogenase from Bacillus cereus to make achievable an up to 10,000-fold regeneration of NADH per cycle of discontinuous conversion. Under suitoble conditions, 300 g/L of substrate could be converted in yields above 96% in one single batch reaction. 

Pennachio, A., Giordano, A., Rossi, M., and Raia, C.A. (2011) Asymmetric reduction of a-keto esters with Thermus thermophilus NADH-dependent carbonyl reductase using glucose dehydrogenase and alcohol dehydrogenase for cofactor regeneration. Eur. J. Org. Chem., 2011 (23), 4361-4366. 

Another approach is based on the reduction of the pH caused by gluconic acid, a coproduct of the transaminahon reaction, indicated with phenol red [111]. The coproduct pyruvate was removed by a lactate dehydrogenase to lactate to shift the equilibrium of the entire reachon toward the product side. The glucose dehydrogenase deployed to regenerate the needed cofactor NADH generates gluconic acid and leads to a decrease in the pH value (Scheme 29.17b). 

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