Amino acid synthesis substrate channeling

Compounds 296-299 inhibit acetohydroxy acid synthase (AHAS), formerly known as acetolactate synthase. Its activity is not present in animals, but it has been found in all plants where measurements have been attempted. Acetohydroxy acid synthase catalyses the first step in production of branched amino acids (leucine, valine and isoleucine) (Scheme 73), which are obviously needed for the protein synthesis and cell growth. The compounds 296-299 seem to bind within the substrate-access channel of the enzyme, thus blocking a-ketocarboxylate access to the active site. While these herbicides are undoubtedly highly successful, resistance developed due to mutations within AHAS is becoming a serious problem [274, 275]. 

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