Durner J, Gailus V, Böger P
Lehrstuhl für Physiologie und Biochemie der Pflanzen, Universität Konstanz, D-7750 Konstanz, Federal Republic of Germany.
Plant Physiol. 1991 Apr;95(4):1144-9. doi: 10.1104/pp.95.4.1144.
The sulfonylurea herbicide chlorsulfuron and the imidazolinone herbicide imazaquin were shown to be noncompetitive and uncompetitive inhibitors, respectively, of purified acetolactate synthase from barley (Hordeum vulgare L.) with respect to pyruvate. From double-reciprocal plots of the time-dependent biphasic inhibition by chlorsulfuron, an initial apparent inhibition constant of 68 nanomolar was calculated (a 0 to 4 minute assay was used for the initial inhibition), and a final steady-state dissociation constant of 3 nanomolar was estimated. The corresponding constants for imazaquin were 10 and 0.55 micromolar. Specific binding of [(14)C]chlorsulfuron and [(14)C]imazaquin to purified acetolactate synthase from barley and partially purified enzyme from corn (Zea mays L.) could be demonstrated by gel filtration and equilibrium dialysis. Evidence is presented that the binding of the inhibitors to the enzyme follows the previously described mechanism of slow reversibility once excess inhibitor has been removed. However, after formation of the slowly reversible complex and subsequent dissociation, both chlorsulfuron and imazaquin seem to permanently inactivate acetolactate synthase. These results add a new feature to the mode of action of these herbicides with respect to their high herbicidal potency.
磺酰脲类除草剂氯磺隆和咪唑啉酮类除草剂咪草喹分别被证明是大麦（Hordeum vulgare L.）纯化的乙酰乳酸合酶相对于丙酮酸的非竞争性和反竞争性抑制剂。从氯磺隆随时间变化的双相抑制的双倒数图中，计算出初始表观抑制常数为68纳摩尔（初始抑制采用0至4分钟的测定），最终稳态解离常数估计为3纳摩尔。咪草喹的相应常数分别为10和0.55微摩尔。通过凝胶过滤和平衡透析可以证明[(14)C]氯磺隆和[(14)C]咪草喹与大麦纯化的乙酰乳酸合酶和玉米（Zea mays L.）部分纯化的酶的特异性结合。有证据表明，一旦去除过量的抑制剂，抑制剂与酶的结合遵循先前描述的缓慢可逆机制。然而，在形成缓慢可逆复合物并随后解离后，氯磺隆和咪草喹似乎都会使乙酰乳酸合酶永久失活。这些结果为这些除草剂的作用方式增添了一个新特点，即它们具有高除草效力。
