Abstract: A new kind of asymmetric hydrogenation reaction catalyzed by Rhodobacter sphaeroides and the reaction mechanism have been studied. The advantages are that coenzyme (NADPH) can be regenerated in situ by the photosynthetic electron-transfer reactions of photosynthetic bacteria relying on light energy, and ketone compounds can be chiraly hydrogenated. Acetophenone was selected as the model substrate, and the whole cell catalytic system, the asymmetric reduction system of redox enzymes and the chromatophore coupled with redox enzymes system were built through preparation of chromatophore and isolation and purification of endocellular (S)-redox enzymes and (R)-redox enzymes of photosynthetic bacteria Rhodobacter sphaeroides. This result indicates that these cells have the capacity of capturing light energy to generate NADPH through photosynthetic electron-transfer reactions and the relative enzymatic activities. (S)-redox enzyme and (R)-redox enzyme were largely influenced by the amount of light in the environment. Effect of the electron donors and hydrogen donors on chemical yield in the reaction system was determined. A novel method for stereochemical control of the asymmetric reduction by photosynthetic bacteria was also reported. Enantioselectivity in asymmetric reduction of acetophenone was improved by illumination with fluorescent light. As a result, the yield of asymmetric reduction reaction was largely improved through promoting coenzyme NADPH regeneration.

Key words: Rhodobacter sphaeroides, redox enzyme, light-controlled asymmetric reduction, acetophenone, phenylethyl alcohol, chromatophore