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-beta-D-glucuronide by beta-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 beta-glucuronidase inhibitor, saccharic acid 1,4-lactone, significantly reduced the H2O2-metabolizing ability of the Scutellaria cells, indicating that beta-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 beta-glucuronidase, cell wall peroxidases, and baicalein pre-exist in Scutellaria cells, their constitutive presence enables the cells to rapidly induce the H2O2-metabolizing system.
Morimoto
S
S
Faculty of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-82, Japan. morimoto@shoyaku.phar.kyushu- u.ac.jp
Tateishi
N
N
Matsuda
T
T
Tanaka
H
H
Taura
F
F
Furuya
N
N
Matsuyama
N
N
Shoyama
Y
Y
D002473:Cell Wall / Q000201:enzymology; D002852:Chromatography, Ion Exchange; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000378:metabolism; D005966:Glucuronidase / Q000037:antagonists & inhibitors; D006861:Hydrogen Peroxide / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D010544:Peroxidases / Q000302:isolation & purification* / Q000378:metabolism; D059828:Plant Cells; D010944:Plants / Q000201:enzymology / Q000378:metabolism*
D004791:Enzyme Inhibitors; D005419:Flavonoids; D006861:Hydrogen Peroxide; D010544:Peroxidases; D005966:Glucuronidase