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首页> 外文期刊>Biochemistry >Allosteric activation of Arabidopsis threonine synthase by S-adenosylmethionine
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Allosteric activation of Arabidopsis threonine synthase by S-adenosylmethionine

机译：S-腺苷甲硫氨酸对拟南芥苏氨酸合酶的变构活化

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摘要

Plant threonine synthase, in contrast to its bacterial counterpart, is strongly stimulated by S-adenosylmethionine via a noncovalent interaction [Giovanelli et al. (1984) Plant. Physiol. 76, 285-292]. The mechanism of activation remained, however, largely unknown. To further characterize this unusual role for S-adenosylmethionine, the Arabidopsis thaliana threonine synthase was overexpressed in Escherichia coli, purified to homogeneity, and then used for kinetic and enzyme-bound pyridoxal 5'-phosphate fluorescence equilibrium-binding experiments. We observed that the activating effect of S-adenosylmethionine results from an 8-fold increase in the rate of catalysis and from a 25-fold decrease in the K-m value for the O-phosphohomoserine substrate. The data can be well fitted by a kinetic model assuming binding of two S-adenosylmethionine molecules on the native enzyme. We suggest that the dramatic modifications of the enzyme kinetic properties originate most presumably from an allosteric and cooperative transition induced by S-adenosylmethionine. This transition occurs at a much faster rate in the presence of the substrate than in its absence. [References: 29]
机译：与植物的苏氨酸合酶相比，植物苏氨酸合酶通过非共价相互作用被S-腺苷甲硫氨酸强烈刺激[Giovanelli等。 （1984）植物。生理学。 76，285-292]。然而，激活机制仍然未知。为了进一步表征这种对于S-腺苷甲硫氨酸的非同寻常的作用，拟南芥苏氨酸合酶在大肠杆菌中过表达，纯化至均一，然后用于动力学和酶结合的吡ido醛5'-磷酸荧光平衡结合实验。我们观察到，S-腺苷甲硫氨酸的活化作用是由于O-磷酸高丝氨酸底物的催化速率增加了8倍，而K-m值降低了25倍。假设两个S-腺苷甲硫氨酸分子结合在天然酶上，则动力学模型可以很好地拟合数据。我们建议，酶动力学特性的戏剧性修改最有可能源自S-腺苷甲硫氨酸引起的变构和协同跃迁。在没有基材的情况下，这种转变发生的速度要比没有基材的情况下快得多。 [参考：29]

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