Acetohydroxyacid synthase (AHAS, EC ) catalyses the first step in branched-chain amino acid biosynthesis and is the target for sulfonylurea and imidazolinone herbicides, which act as potent and specific inhibitors. Mutants of the enzyme have been identified that are resistant to particular , the selectivityof thesemutants towards various sulfonylureas and imidazolinones has not been determined systematically. Now that the structure of the yeast enzyme isknown, both in theabsenceandpresenceof a bound herbicide, a detailed understanding of the molecular interactions between the enzyme and its inhibitors becomes possible. .
