Metabolic deactivation of the herbicide thiazopyr by animal liver esterases.

1. Thiazopyr was hydrolysed in vitro to its corresponding acid by rabbit and porcine liver esterases. 2. A wide range of thiazopyr esterase activity was observed in extracts from liver acetone powders from 15 animal species with bovine, rabbit and pigeon showing the highest activities. 3. Using soybean tissue culture cells and Arabidopsis seedlings, the acidic metabolite was shown to possess < 1% of the herbicidal activity of thiazopyr. 4. We propose that biotransformation of thiazopyr to the acid is a critical pathway of metabolism in animals and plants.