A bi-enzymatic system for efficient enantioselective bioconversion of racemic mandelic acid

(S)-Mandelate dehydrogenase (SMDH) from Pseudomonas aeruginosa is a FMN-dependent enzyme and catalyze the oxidation of (S)-mandelic acid to benzoylformic acid (BA), resulting in the reduction of FMN. Laccase catalyze the conversion of ferrocyanide to ferricyanide meanwhile oxygen is reduced to water. We report a coupled, bi-enzyme system consisting of SMDH, laccase and the ferro-/ferricyanide redox couple, leading to the enantioselective bioconversion of racemic mandelic acid. The SMDH, optimal pH was about 6.5 and optimal temperature was about 30 ̊C, was extracted from a recombinant E. coli. The laccase, optimal pH was about 3.0 and optimal temperature was about 30 ̊C, was extracted from Agaricus bisporus. The calculated Michaelis constant (Km) of SMDH for racemic mandelic acid is 0.92 mM and ferricyanide 3.87 mM; the Km value of laccase for ferrocyanide is 0.12 mM. In the coupling reaction, the conversion of (S)-mandelic acid was close to complete within 12 h at 30 ̊C, pH 6.5, 140 rpm. The enantiomeric excess value of (R)-mandelic acid as a production exceeded 99%.