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

Abstract

Abstract ( 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 ( K m ) of SMDH for racemic mandelic acid is 0.92 mM and ferricyanide 3.87 mM; the K m 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%.