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 (CO2)-C-14. The bleaching herbicide sulcotrione [2-(2-chloro-4-methanesulfonyl-benzoyl)-1,3-cyclohexanedione] was shown to be a potent, linear competitive inhibitor of 4-hydroxyphenylpyruvate dioxygenase. Kinetic analyses determined that the K-m for the substrate, 4-hydroxyphenylpyruvate, was 4.3 mu M, and the K-i value was 9.8 nM for sulcotrione.