Novel hydrogen peroxide metabolism in suspension cells of Scutellaria baicalensis Georgi

We identified a rapid and novel system to effectively metabolize a large amount of H₂O₂ in the suspension cells of Scutellaria baicalensis Georgi. In response to an elicitor, the cells immediately initiate the hydrolysis of baicalein 7-O-β-D-glucuronide by β-glucuronidase, and the released baicalein is then quickly oxidized to 6,7-dehydrobaicalein by peroxidases. Hydrogen peroxide is effectively consumed during the peroxidase reaction. The β-glucuronidase inhibitor, saccharic acid 1,4-lactone, significantly reduced the H₂O₂-metabolizing ability of the Scutellaria cells, indicating that β- glucuronidase, which does not catalyze the H₂O₂ degradation, plays an important role in the H₂O₂ metabolism. As H₂O₂-metabolizing enzymes, we purified two peroxidases using ammonium sulfate precipitation followed by sequential chromatography on CM-cellulose and hydroxylapatite. Both peroxidases show high H₂O₂-metabolizing activity using baicalein, whereas other endogenous flavones are not substrates of the peroxidase reaction. Therefore, baicalein predominantly contributed to H₂O₂ metabolism. Because β-glucuronidase, cell wall peroxidases, and baicalein pre-exist in Scutellaria cells, their constitutive presence enables the cells to rapidly induce the H₂O₂-metabolizing system.