Relationships among the herbicide and functional sites of acetohydroxy acid synthase from Chlorella emersonii |
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Authors: | Dorit Landstein Shoshana Arad Ze'ev Barak David M Chipman |
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Institution: | (1) Department of Life Sciences and Institutes for Applied Research, Ben-Gurion University of the Negev, PO Box 653, 84-105 Beer-Sheva, Israel |
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Abstract: | The properties of acetohydroxy acid synthase (AHAS, EC 4.1.3.18) 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 (K
m, 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.Abbreviations AHAS
acetohydroxy acid synthase
- AL
acetolactate
- AHB
acetohydroxybutyrate
- IM
imazapyr
- TP
triazolopyrimidine sulfonanilide herbicide XRD-498
- R
enzyme specificity
- SMM
sulfometuron methyl
This research was supported in part by the United States — Israel Binational Science Foundation (BSF), Jerusalem, Israel (Grant 86-00205) and the Fund for Basic Research, Israel Academy of Sciences. |
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Keywords: | Acetolactate synthase Chlorella (mutant) Imidazolinone Mutant (herbicide resistance) Sulfonylurea Triazolopyrimidine sulfonanilide |
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