Relationships among the herbicide and functional sites of acetohydroxy acid synthase from Chlorella emersonii

Dorit Landstein, Shoshana (Malis) Arad, Ze'ev Barak, David M. Chipman

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


The properties of acetohydroxy acid synthase (AHAS, EC from wild-type Chlorella emersonii (var. Emersonii, CCAP-211/11n) and two spontaneous sulfometuron methyl (SMM)-resistant mutants were examined. The AHAS from both mutants was resistant to SMM and cross-resistant to imazapyr (IM) and the triazolopyrimidine sulfonanilide herbicide XRD-498 (TP). The more-SMM-resistant mutant had AHAS with altered catalytic parameters (Km, specificity), but unchanged sensitivity to the feedback inhibitors valine and leucine. The second mutant enzyme was less sensitive to the feedback inhibitors, but had otherwise unchanged kinetic parameters. Inhibition-competition experiments indicated that the three herbicides (SMM, IM, TP) bind in a mutually exclusive manner, but that valine can bind simultaneously with SMM or TP. The three herbicide classes apparently bind to closely overlapping sites. We suggest that the results with C. emersonii and other organisms can all be explained if there are separate binding sites for herbicides, feedback inhibitors and substrates.

Original languageEnglish
Pages (from-to)1-6
Number of pages6
Issue number1
StatePublished - 1 Jul 1993


  • Acetolactate synthase
  • Chlorella (mutant)
  • Imidazolinone
  • Mutant (herbicide resistance)
  • Sulfonylurea
  • Triazolopyrimidine sulfonanilide

ASJC Scopus subject areas

  • Genetics
  • Plant Science


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