Regioselective hydroxylation of isoflavones by Streptomyces avermitilis MA-4680(MICROBIAL PHYSIOLOGY AND BIOTECHNOLOGY)

Screening of bacterial whole cells was performed for regioselective hydroxylation of daidzein and genistein. Among the strains examined, Streptomyces avermitilis MA-4680 showed high ortho-dihydroxylation activity to produce 3',4',7-trihydroxyisoflavone and 3',4',5,7-tetrahydroxyisoflavone from daidzein (4',7-dihydroxyisoflavone) and genistein (4',5,7-trihydroxyisoflavone), respectively. Using 100mg cells (wet wt.) and 1% (v/v) Triton ×100 in 1ml of total reaction volume, where 100μl of the substrate solution (0.5mM in 10% (v/v) mixed solvent of DMSO:MeOH=3:7) was added to 900μl of potassium phosphate buffer (100mM, pH7.2), a 16% molar conversion yield of 3',4',7-trihydroxyisoflavone was obtained from 0.5mM daidzein after 24h of reaction time at 28℃ and 200rpm. Ketoconazole significantly (ca. 90%) inhibited the ortho-hydroxylation activity of daidzein, suggesting that cytochrome P450 enzymes putatively play roles in regiospecific daidzein hydroxylation. The analysis of the reaction products was determined by gas chromatography/mass spectrometry (GC/MS) and ^1H NMR.