Cytochrome P450 monooxygenases herbicides

T.J. Fleischmann, and R.E. Dewey (1999). Expression of a soybean cytochrome P450 monooxygenase cDNA in yeast and tobacco enhances the metabolism of phenylurea herbicides. Proc. Natl Acad. Sci USA 96, 1750-1755. 

NA had also a stimulatory effect on the oxidative metabolism of the herbicide bentazone. Microsomal preparations of etiolated shoots from maize, which had received a seed treatment with NA, showed activity of a bentazone hydroxylase, which was not detectable in extracts from controls without safener pre-treatment [35]. Also, the improved tolerance of maize to the imidazolinone AC263222 after NA seed treatment could be related to enhanced AC 263222 hydroxylation by stimulation of a cytochrome P450 monooxygenase [31]. 

Cytochrome P450 monooxygenases (CYP) are membrane-bound enzymes that catalyze the addition of oxygen to hydrophobic compounds. CYPs are important enzymes in plant secondary metabolism however, they are also important in selectivity of a large numbor of hmbicides, particularly in cereals (70). CYPs catalyze a variety of reactions, but the most important ones for herbicide detoxification are hydroxylations and dealkylations (Figure 3). Ring hydroxylation reactions frequently render herbicides inactive however, dealkylation reactions may only partially detoxify herbicides. 

Figure 3. Examples of herbicide detoxification reactions catalyzed by cytochrome P450 monooxygenases.

---