Inhibition of Barnyardgrass 4-Hydroxyphenylpyruvate Dioxygenase by Sulcotrione

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27) was partially purified from barnyardgrass (Echinochloa crus-galli L.) leaves and assayed by high-performance liquid chromatography analysis of product formation or by the capture of released 14CO2. The bleaching herbicide sulcotrione [2-(2-chloro-4-methanesulfonylbenzoyl)-1,3-cyclohexanedione] was shown to be a potent, linear competitive inhibitor of 4-hydroxyphenylpyruvate dioxygenase. Kinetic analyses determined that the Km for the substrate, 4-hydroxyphenylpyruvate, was 4.3 [mu]M, and the Ki value was 9.8 nM for sulcotrione.