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 s tudied. Baker's yeast-mediated bioreduction of carbonyl compounds coup led with the oxidative pathway of ethanol is efficient and clean compa red with the earlier procedure using carbohydrates as the energy sourc e. To study NADH regeneration, the bioreduction of acetol catalyzed by NADH-dependent carbonyl-reducing enzymes was examined by using ethano l or acetate as the energy source under several aeration conditions, i ncluding an anaerobic environment. The results suggested that NAD+ for med on the reduction of the carbonyl group was mainly regenerated as N ADH through alcoholic oxidation into acetate. NADPH regeneration was t hen studied in the same manner by examining the bioreduction of ethyl acetoacetate catalyzed by NADPH-dependent carbonyl-reducing enzymes. T he results suggested that NADPH was regenerated through acetate oxidat ion into carbon dioxide. Thus, a total scheme for NAD(P)H regeneration using ethanol as the energy source, coupled with bioreduction, was pr oposed.