Abstract
Arogenate dehydratase (ADT) catalyzes the last step of phenylalanine (Phe) biosynthesis in plants. A gene,OsPDTH, that is rice homolog of bacterial prephenate dehydratase, was identified from rice mutant (MTR1) as a mutation point. This mutation is responsible for resistance to 5-metyltryptophan and high levels of Phe accumulation. We characterized OsPDTH using a wheat embryo cell-free system, and clarified its function as ADT. In vitro chloroplast import assay revealed that the OsPDTH protein translocates into chloroplasts. Kinetic analysis revealed that OsPDTH showed high substrate affinity to arogenate over ten times more than that to prephenate. ADT activity of OsPDTH was feedback-inhibited by Phe, and the mutant enzyme showed resistance to Phe. We concluded that high-level accumulation of Phe in the MTR1 is ascribable to the insensitivity of the mutant ADT to Phe.
