β-Glucuronidase from callus cultures of Scutellaria baicalensis Georgi was purified to apparent homogeneity by fractionated ammonium-sulfate precipitation and chromatography on diethylaminoethyl-cellulose, hydroxylapatite and baicalin-conjugated Sepharose 6B. A 650-fold purification was obtained by this purification system. When subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis the purified protein migrated as a single band with a molecular mass of 55 kDa. We determined that the native enzyme has a molecular mass of 230 kDa using gel-filtration chromatography. These results suggested that the enzyme exists as a homotetramer composed of four identical 55-kDa subunits. The enzyme showed a broad pH optimum between 7.0 and 8.0. The Km values were 9 μM, 10 μM, 30 μM and 40 μM for luteolin 3′ -O-β-d-glucuronide, baicalin, wogonin 7-O-β-d-glucoronide and oroxlin 7-O-β-d-glucuronide, respectively. The enzyme was most active with flavone 7-O-β-d-glucuronides.
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