Studies on Herbicide Design through Mutation on Herbicidal Target Acetohydroxyacid Synthase (Ⅱ). Effects of mutagenesis at tryptophan 464 of Escherichia coli acetohydroxyacid synthase Ⅱ on herbicidal molecules

Acetohydroxyacid synthase (AHAS) is a target for sulfonylurea and imidazolinone herbicides. Resistance to sulfonylurea and imidazolinone herbicides can occur by mutation in AHAS. Four E. coli AHAS Ⅱ mutants (W464A, W464F, W464L, W464Y) and wild type were characterized for the sensitivities to commercial inhibitors (chlorimuron ethyl, chlorsulfuron, imazethapyr, imazaquin) and some newly synthesized alkylthio-containing sulfonylureas. Wild type enzyme showed it was sensitive to these herbicidal compounds. The mutants showed they were resistant to the commercial sulfonylureas with the increases of Kappi values from dozens to several thousand fold. Substantial differences wereobserved in the sensitivity of wild type and mutant enzymes to these various inhibitors. Alkylthio-containing sulfonylureas seem they met relatively weak resistance by W464 mutant enzymes.