LOW BARRIER HYDROGEN BONDS IN ENZYMIC CATALYSIS

这个项目的目的是寻找实验证据来 支持最近的假设，即酶能获得所需的能量 通过形成非常强的、低势垒的氢键来催化 过渡态，或在其他不稳定的中间体中，而 在基态只有微弱的氢键。低门槛 氢键具有非常低的场质子核磁共振化学位移，我们 将在酶复合体中寻找如此低场的信号，在那里我们 从其他证据来看，他们应该在场。例如, 我们将看到富马酸酶与氯富马酸的复合， 3-硝基-乳酸或3-硝基-丙酸酯，因为这类络合物应该 在我们的反应中模仿烯化的“碳负离子”中间体 相信必须通过低势垒氢键来稳定。低门槛 氢键也有较低的氢分馏系数，这 可以通过积分混合H2O和D2O中的核磁共振峰来测量 溶剂型。我们将测量任何低场的分馏系数。 我们在富马酸酶复合体中发现的峰，以及分馏 以前在核磁共振谱中看到的低场峰的因子 天冬氨酸转氨酶。

The purpose of this project is to seek experimental evidence to support the recent hypothesis that enzymes obtain the energy needed for catalysis by forming very strong, low-barrier, hydrogen bonds in the transition state, or in otherwise unstable intermediates, while having only weak hydrogen bonds in the ground state. Low-barrier hydrogen bonds have very low field proton NMR chemical shifts, and we will look for such low field signals in enzyme complexes where we think, from other evidence, that they should be present. For example, we will look at fumarase complexed with chlorofumarate, 3-nitrolactate, or 3-nitropropionate, since such complexes should mimic the enolized "carbanion" intermediate in the reaction which we believe must be stabilized by low-barrier hydrogen bonds. Low-barrier hydrogen bonds also have low deuterium fractionation factors, which can be measured by integrating the NMR peaks in mixed H2O and D2O solvent. We will measure the fractionation factors of any low field peaks we find in fumarase complexes, and also the fractionation factors of the low field peaks previously seen in the NMR spectra of aspartate transaminase.