title: Cytochrome P450-catalyzed brassinosteroid pathway activation through synthesis of castasterone and brassinolide in Phaseolus vulgaris.
abstract: The last reaction in the biosynthesis of brassinolide has been examined enzymatically. A microsomal enzyme preparation from cultured cells of Phaseolus vulgaris catalyzed a conversion from castasterone to brassinolide, indicating that castasterone 6-oxidase (brassinolide synthase) is membrane associated. This enzyme preparation also catalyzed the conversions of 6-deoxocastasterone and typhasterol to castasterone which have been reported to be catalyzed by cytochrome P450s, CYP85A1 of tomato and CYP92A6 of pea, respectively. The activities of these enzymes require molecular oxygen as well as NADPH as a cofactor. The enzyme activities were strongly inhibited by carbon monoxide, an inhibitor of cytochrome P450, and this inhibition was recovered by blue light irradiation in the presence of oxygen. Commercial cytochrome P450 inhibitors including cytochrome c, SKF 525A, 1-aminobenzotriazole and ketoconazole also inhibited the enzyme activities. The present work presents unanimous enzymological evidence that cytochrome P450s are responsible for the synthesis of brassinolide from castasterone as well as of castasterone from typhasterol and 6-deoxocastasterone, which have been deemed activation steps of BRs.
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul 156-756, South Korea.
authors.forename: Tae-Wuk
authors.initials: TW
authors.lastname: Kim
authors.forename: Soo Chul
authors.initials: SC
authors.lastname: Chang
authors.forename: June Seung
authors.initials: JS
authors.lastname: Lee
authors.forename: Baik
authors.initials: B
authors.lastname: Hwang
authors.forename: Suguru
authors.initials: S
authors.lastname: Takatsuto
authors.forename: Takao
authors.initials: T
authors.lastname: Yokota
authors.forename: Seong-Ki
authors.initials: SK
authors.lastname: Kim
mesh_terms: D060406:Brassinosteroids; D002248:Carbon Monoxide / Q000494:pharmacology; D002384:Catalysis; D002777:Cholestanols / Q000378:metabolism*; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism* / Q000528:radiation effects; D003600:Cytosol / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008401:Gas Chromatography-Mass Spectrometry; D008027:Light; D008861:Microsomes / Q000201:enzymology; D009249:NADP / Q000494:pharmacology; D010084:Oxidation-Reduction; D010100:Oxygen / Q000494:pharmacology; D027805:Phaseolus / Q000201:enzymology* / Q000378:metabolism; D010840:Phytosterols / Q000378:metabolism*; D013260:Steroids, Heterocyclic / Q000378:metabolism*
chemical_list: D060406:Brassinosteroids; D002777:Cholestanols; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D010840:Phytosterols; D013260:Steroids, Heterocyclic; D009249:NADP; D002248:Carbon Monoxide; C083545:castasterone; D003577:Cytochrome P-450 Enzyme System; D010100:Oxygen; C023623:brassinolide