Abstract
The major catabolic pathway of abscisic acid (ABA) is initiated by hydroxylation at C-8' by ABA 8'-hydroxylase. Recently, Arabidopsis CYP707A genes have been shown to encode ABA 8'-hydroxylases. We examined the structural requirements for substrate recognition of ABA 8'-hydroxylase using 45 ABA analogs. The analogs were incubated with a microsomal fraction of CYP707A3 expressing insect cells, and all analogs were tested for their ability to act as an inhibitor. ABA 8'-hydroxylase recognized strictly the C-8' and C-9' in ABA. The carboxyl group at C-1 was necessary for binding to the enzyme, whereas C-6 and 1'-hydroxyl group were not essential for effective binding. The lack or enlargement of C-7' and the substitution at C-3' affected the binding to the enzyme, although it is not necessarily fatal. The present findings will be useful for developing the inhibitors of ABA 8'-hydroxylase.
