NAD(P)H REGENERATION USING ETHANOL AS AN ENERGY-SOURCE IN BAKERS YEAST-MEDIATED BIOREDUCTION

A scheme for NAD(P)H regeneration from the corresponding oxidized form through the oxidative pathway of ethanol in baker's yeast cells was studied. Baker's yeast-mediated bioreduction of carbonyl compounds coupled with the oxidative pathway of ethanol is efficient and clean compared with the earlier procedure using carbohydrates as the energy source. To study NADH regeneration, the bioreduction of acetol catalyzed by NADH-dependent carbonyl-reducing enzymes was examined by using ethanol or acetate as the energy source under several aeration conditions, including an anaerobic environment. The results suggested that NAD+ formed on the reduction of the carbonyl group was mainly regenerated as NADH through alcoholic oxidation into acetate. NADPH regeneration was then studied in the same manner by examining the bioreduction of ethyl acetoacetate catalyzed by NADPH-dependent carbonyl-reducing enzymes. The results suggested that NADPH was regenerated through acetate oxidation into carbon dioxide. Thus, a total scheme for NAD(P)H regeneration using ethanol as the energy source, coupled with bioreduction, was proposed.