title: Differences between the structural requirements for ABA 8'-hydroxylase inhibition and for ABA activity.
abstract: A major catabolic enzyme of the plant hormone abscisic acid (ABA) is the cytochrome P450 monooxygenase ABA 8'-hydroxylase. For designing a specific inhibitor of this enzyme, the substrate specificity and inhibition of CYP707A3, an ABA 8'-hydroxylase from Arabidopsis thaliana, was investigated using 45 structural analogues of ABA and compared to the structural requirements for ABA activity. Substrate recognition by the enzyme strictly required the 6'-methyl groups (C-8' and C-9'), which were unnecessary for ABA activity, whereas elimination of the 3-methyl (C-6) and 1'-hydroxyl groups, which significantly affected ABA activity, had little effect on the ability of analogues to competitively inhibit the enzyme. Fluorination at C-8' and C-9' resulted in resistance to 8'-hydroxylation and competitive inhibition of the enzyme. In particular, 8',8'-difluoro-ABA and 9',9'-difluoro-ABA yielded no enzyme reaction products and strongly inhibited the enzyme (K(I) = 0.16 and 0.25 microM, respectively).
authors.affiliation: Department of Applied Biological Chemistry, Faculty of Agriculture, Shizuoka University, Shizuoka 422-8529, Japan.
authors.forename: Kotomi
authors.initials: K
authors.lastname: Ueno
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Araki
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Hirai
authors.forename: Shigeki
authors.initials: S
authors.lastname: Saito
authors.forename: Masaharu
authors.initials: M
authors.lastname: Mizutani
authors.forename: Kanzo
authors.initials: K
authors.lastname: Sakata
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Todoroki
mesh_terms: D000040:Abscisic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D017360:Arabidopsis / Q000737:chemistry / Q000201:enzymology*; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry*; D004789:Enzyme Activation / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018525:Germination / Q000187:drug effects; D006900:Hydroxylation / Q000187:drug effects; D007700:Kinetics; D018545:Lactuca / Q000737:chemistry; D008861:Microsomes / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000737:chemistry*; D012275:Oryza / Q000737:chemistry; D010937:Plant Growth Regulators / Q000494:pharmacology*; D010940:Plant Proteins; D011487:Protein Conformation / Q000187:drug effects; D036226:Seedlings / Q000737:chemistry / Q000166:cytology / Q000187:drug effects; D013379:Substrate Specificity
chemical_list: D004791:Enzyme Inhibitors; D010937:Plant Growth Regulators; D010940:Plant Proteins; D000040:Abscisic Acid; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C107203:abscisic acid 8'-hydroxylase