NOVEL HYDROGEN-PEROXIDE METABOLISM IN SUSPENSION CELLS OF SCUTELLARIA-BAICALENSIS GEORGI

We identified a rapid and novel system to effectively metabolize a lar ge amount of H2O2 in the suspension cells of Scutellaria baicalensis G eorgi. In response to an elicitor, the cells immediately initiate the hydrolysis of baicalein 7-O-beta-D-glucuronide by beta-glucuronidase, and the released baicalein is then quickly oxidized to 6,7-dehydrobaic alein by peroxidases. Hydrogen peroxide is effectively consumed during the peroxidase reaction. The beta-glucuronidase inhibitor, saccharic acid 1,4-lactone, significantly reduced the H2O2-metabolizing ability of the Scutellaria cells, indicating that beta-glucuronidase, which do es not catalyze the H2O2 degradation, plays an important role in the H 2O2 metabolism. As H2O2-metabolizing enzymes, we purified two peroxida ses using ammonium sulfate precipitation followed by sequential chroma tography on CM-cellulose and hydroxylapatite. Both peroxidases show hi gh H2O2-metabolizing activity using baicalein, whereas other endogenou s flavones are not substrates of the peroxidase reaction. Therefore, b aicalein predominantly contributed to H2O2 metabolism. Because beta-gl ucuronidase, cell wall peroxidases, and baicalein pre-exist in Scutell aria cells, their constitutive presence enables the cells to rapidly i nduce the H2O2-metabolizing system.