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Acetolactate Synthase

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Csaba Cseke – One of the best experts on this subject based on the ideXlab platform.

Jung Do Choi – One of the best experts on this subject based on the ideXlab platform.

  • amino acid residues conferring herbicide tolerance in tobacco Acetolactate Synthase
    Biochemical and Biophysical Research Communications, 2000
    Co-Authors: Chom-kyu Chong, Jung Do Choi
    Abstract:

    Acetolactate Synthase (ALS) is the common enzyme in the biosynthetic pathways leading to valine, leucine, and isoleucine in plants and microorganisms. ALS is the target site of several classes of structurally unrelated herbicides including sulfonylureas, imidazolinones, and triazolopyrimidines. To identify the residues conferring herbicide tolerance in tobacco ALS, site-directed mutamutagenesis for three residues, Ala121, Pro187 and Ser652, was performed. Mutant A121T showed strong resistance to Londax (a sulfonylurea) and Cadre (an imidazolinone), while mutant S652T was resistant only to Cadre. The S652N mutation abolished the binding affinity of FAD, and inactivated the enzyme. Double mutation of Ala121 and Ser652 with Thr yielded a mutant highly tolerant to Londax, Cadre, and TP (a triazolopyrimidine sulfonamide), but has enzymatic properties similar to those of wild-type. Substitution of Pro187 with Ser resulted in the enzyme highly susceptible to oxidation and fragmentation. These results suggest that two residues Ala121 and Ser652 are potent residues conferring herbicide resistance in tobacco ALS, and that double mutation of Ala121 and Ser652 by Thr can confer stronger tolerance to Londax, Cadre, and TP.

  • Role of Tryptophanyl Residues in Tobacco Acetolactate Synthase
    Biochemical and biophysical research communications, 1999
    Co-Authors: Chom-kyu Chong, Hee-jee Shin, Soo-ik Chang, Jung Do Choi
    Abstract:

    Abstract Acetolactate Synthase (ALS) catalyzes the first common step in the biosynthesis of valine, leucine, and isoleucine. ALS is the target of three classes of herbicides, the sulfonylureas, the imidazolinones, and the triazolopyrimidines. Five mutants (W266F, W439F, W490F, W503F, and W573F) of the ALS gene from Nicotiana tabacum were constructed and expressed in Escherichia coli, and the enzymes were purified. The W490F mutation abolished the binding affinity for cofactor FAD and inactivated the enzyme. The replacement of Trp573 by Phe yielded a mutant ALS resistant to the three classes of herbicides. The other three mutations, W266F, W439F, and W503F, did not significantly affect the enzymatic properties and the sensitivity to the herbicides. These results indicate that the Trp490 residue is essential for the binding of FAD and that Trp573 is located at the herbicide binding site. The data also suggest that the three classes of herbicides bind ALS competitively.

  • Inhibition of Barley Acetolactate Synthase by Triazolopyrimidine Derivative
    Journal of The Korean Chemical Society, 1999
    Co-Authors: Sung Ho Kim, Soo-ik Chang, Sung Keon Namgoong, Jung Hyu Shin, Jung Do Choi
    Abstract:

    Acetolactate Synthase (ALS) catalyzes the first common reaction in the biosynthesis of branched-chain amino acids, valine, leucine, and isoleucine. ALS is the common target of several classes of structurally diverse herbicides, the triazolopyrimidines, the imidazolinones, the sulfonylureas, and pyrimidyl-oxy-benzoates. We examined ihibitory activities of newly synthesized triazolopyrimidine sulfonamide derivatives using partially purified ALS from barley. values for the active derivatives are 0.5nM∼8M. Among them TP1 and TP2 are the most potent ALS inhibitors with values of 0.5nM and 1.6nM, respectively. These inhibitors are more potent in the inhibition of barley ALS than commercial herbicides, Metosulam (;3.6 nM), Flumetsulam (;126 nM), and Cadre (). The progress curves for inhibition of ALS by TP2 showed that the amount of inhibition increases with time. The inhibition of ALS by TP2 was mixed-type inhibition with respect to pyruvate. Dual inhibition analyses of TP2 versus an imidazolinone, Cadre, and Leu showed parallel and intercepting kinetic pattern, respectively. The results suggest that TP2 binds to ALS competively with Cadre but not with Leu. Chemical modification of cysteinly residues in ALS decreased the sensitivity of ALS to Leu, while the modification did not affect the sensitivity of ALS to TP2 and Cadre.

Peter Böger – One of the best experts on this subject based on the ideXlab platform.

M. Paula Watt – One of the best experts on this subject based on the ideXlab platform.

Paul R Schmitzer – One of the best experts on this subject based on the ideXlab platform.

  • lack of cross resistance of imazaquin resistant xanthium strumarium Acetolactate Synthase to flumetsulam and chlorimuron
    Plant Physiology, 1993
    Co-Authors: Paul R Schmitzer, Robert J Eilers, Csaba Cseke
    Abstract:

    Acetolactate Synthase (ALS) was isolated from a field population of cocklebur (Xanthium strumarium) that developed resistance to the herbicide Scepter following three consecutive years of application. The active ingredient of Scepter, imazaquin, gave an inhibitor concentration required to produce 50% inhibition of the enzyme activity that was more than 300 times greater for the resistant enzyme than for the wild-type cocklebur ALS. Tests with flumetsulam and chlorimuron show that the resistant ALS was not cross-resistant to these two other classes of ALS inhibitors.