Stereospecific hydrogenation of the CC double bond of enones by Escherichia coli overexpressing an enone reductase of Nicotiana tabacum

We examined the biotransformation of enantiomeric pairs of enones such as pulegone and carvone in recombinant Escherichia coli expressing Nicotiana tabacum pulegone reductase. It was found that recombinant E. coli cells acquired the ability for stereospecific hydrogenation of the exocyclic CC double bond of pulegone. However, stereospecificity in hydrogenation with the recombinant E. coli cells was opposite to that in hydrogenation with N. tabacum cells. On the other hand, the isolated recombinant pulegone reductase (rPRase) from the recombinant E. coli cells catalyzed hydrogenation of the exocyclic CC double bond of pulegone; the hydrogen atoms participating in the reduction at C-8 and C-4 of pulegone originate from the pro-4R hydrogen of NADPH and the medium (H2O), respectively. Stereospecificity was lost in the hydrogenation of pulegone with the isolated rPRase, but was recovered when bovine serum albumin was added to the enzymatic reaction as an auxiliary factor.