Studies on Herbicide Design through Mutation on Herbicidal Target ——Acetohydroxyacid Synthase(I). Enzyme kinetics of wild type and mutants of E. coli AHAS II

To investigate the interaction of various mutation forms of acetohydroxyacid synthase (AHAS) with herbicides and study the mechanism of herbicide resistance, a series of W464 mutated AHAS isoenzyme II were constructed by megaprimer method. DNA sequencing showed that the four mutants of E. coli AHAS II are successfully constructed. These purified mutants have different properties on different enzyme cofactors, such as pyruvate, ThDP, FAD and Mg2+, compared to that of the wild type. The influences on Kc of FAD and Mg2+ by mutants showed the same trend: Wild-type > W464F > W464L > W464A >W464Y; while that of pyruvate and ThDP showed more dramatic changes. The systematic study on enzyme kinetics of wild type and mutant AHAS provides information for inhibition and resistant mechanism of herbicidal molecules on the target enzyme.