Purification and Properties of a Plant β-D-Glucuronidase from Scutellaria Root

beta-D-Glucuronidase (baicalinase, GUS [EC 3.2.1.31]) activity in the crude drug, Scutellaria root, was assayed in line with the quality control standards of Kampo (Japanese Herbal) medicines. GUS was purified to homogeneity in the purification steps including DEAE-Sepharose Fast Flow and chromatofocusing used PBETM94 and Polybuffer 74. These results suggest that the Scutellaria GUS is composed of 55kDa active subunits and that the isoelectric point of this enzyme is pH 5.4. Optimal catalytic activity was found at pH 4.7 in the pH range 3.6--6.2 in 50 mM Na-citrate buffer. The purified enzyme hydrolyzed baicalin and wogonin glucuronide, but did not hydrolyze glycyrrhizin or some beta-glucosides found in other crude drugs. GUS activity in several crude drugs is also described.