Purification and characterization of acetophenone reductase with excellent enantioselectivity from Geotrichum candidum NBRC 4597.

NADH-dependent enzyme reducing acetophenone derivatives with high stereoselectivities and wide substrate specificities from Geotrichum candidum NBRC 4597 was isolated, purified, characterized, and used for asymmetric synthesis. Through five-step purification including ammonium sulfate fractionation and a series of chromatographies, the enzyme was purified about 150-fold with a yield of 5.6%. The active enzyme has a molecular mass of 73 kDa determined by gel filtration chromatography, and the SDS-PAGE result reveals that the molecular size of the subunit is 36 kDa. These results indicate that the enzyme consists of a homodimer of a 36 kDa subunit. The acetophenone reductase exhibited the highest activity at 50 degrees C and optimal pH at 5.5. The enzyme was the most stable at 40 degrees C. No metal ions considerably activated the enzyme, and such metal ions as Cu2+, Cd2+, and Zn2+ strongly inhibited the activity of the enzyme. The Vmax and the apparent Km value of the reductase were 77.0 micromol/min per milligram of protein and 0.296 mM for acetophenone, respectively. The N-terminal and internal amino acid sequences were determined by peptide sequencer. Furthermore, the purified enzyme was used for asymmetric reduction of acetophenone, resulting in the formation of corresponding (S)-alcohol with 99% ee.