同位体アレニウス前因子 (A(H) /A(D)) が単位であるとき,水素トンネル化のための実験的証拠
Sudhir C Sharma1, Judith P Klinman
1Department of Chemistry and Molecular and Cell Biology, University of California, Berkeley, California 94720-1460, USA.
Journal of the American Chemical Society
|December 9, 2008
まとめ
酵素における水素トンネリングを調査したこの研究では,二重変異した大豆リポキシゲナーゼ (SLO-1) が,非古典的な運動同位体効果にもかかわらず,半古典的な反応モデルに挑戦し,単一アーレニウス前因子比を示しています.
科学分野:
- バイオケミストリー バイオケミストリー
- 化学動力学 化学動力学
- 量子力学は,量子力学という
背景:
- 動性同位体効果 (KIE) とその温度依存性は,凝縮相での水素トンネリングの研究に極めて重要です.
- アレニウス前因子 (A(H) /A(D)) の比率が統一に近い水素移転反応は,典型的には半古典的と考えられます.
研究 の 目的:
- 大豆リポキシゲナーゼ (SLO-1) の二重変異体における水素移転のメカニズムを調査する.
- 以前,水素トンネリングを示すことが示された酵素が,ユニットアレニウス前因子比率を持つ非古典的なKIEsを表示できるかどうかを判断する.
主な方法:
- 大豆リポキシゲナーゼ (SLO-1) の二重変異体に関する酵素動力学的研究.
- 運動同位体効果 (KIEs) の温度依存性の分析.
- アレニウス前因子 (A(H) /A(D)) の比率の計算.
主要な成果:
- ダブルミュータントのSLO-1は,アレニウス前因子比 (A(H) / A(D) = 1) の単位を示した.
- 単位比にもかかわらず,酵素は高度に上昇した非古典的な運動同位体効果を示した.
- これは,ユニット比が半古典的な水素移転を示すという一般的な仮定と相反する.
結論:
- 単位のアーレニウス事因数比だけでは,量子力学的な水素トンネリングを排除するには不十分です.
- 酵素工学は,反応機構の伝統的な解釈に挑戦する複雑な運動行動につながる可能性があります.
- 大豆リポキシゲナーゼ変異体は,量子トンネリングと酵素構造の相互作用を研究するためのモデルを提供します.
関連する概念動画
Hess's Law
There are two ways to determine the amount of heat involved in a chemical change: measure it experimentally, or calculate it from other experimentally determined enthalpy changes. Some reactions are difficult, if not impossible, to investigate and make accurate measurements for experimentally. And even when a reaction is not hard to perform or measure, it is convenient to be able to determine the heat involved in a reaction without having to perform an experiment.
Arrhenius Plots
The Arrhenius equation relates the activation energy and the rate constant, k, for chemical reactions. In the Arrhenius equation, k = Ae−Ea/RT, R is the ideal gas constant, which has a value of 8.314 J/mol·K, T is the temperature on the kelvin scale, Ea is the activation energy in J/mole, e is the constant 2.7183, and A is a constant called the frequency factor, which is related to the frequency of collisions and the orientation of the reacting molecules.
The Arrhenius equation can be used to...
The Arrhenius equation can be used to...
¹H NMR of Labile Protons: Deuterium (²H) Substitution
This lesson illustrates the role of deuterium substitution in simplifying the NMR spectrum of compounds comprising labile protons. One method employed is the use of deuterium. Amongst the three isotopes of hydrogen, deuterium (2H) has a nucleus composed of one proton and one neutron. When the D2O solvent is added to a pure dry ethanol solution, its labile proton is substituted with deuterium.
The Bohr Model
Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded by lighter and even tinier electrons continually moving about the nucleus was well established. This picture was called the planetary model since it pictured the atom as a miniature “solar system” with the electrons orbiting the nucleus like planets orbiting the sun. The simplest atom is hydrogen, consisting of a single proton as the nucleus...
Hydrogen Bonds
A hydrogen bond is formed when a weakly positive hydrogen atom already bonded to one electronegative atom (for example, the oxygen in the water molecule) is attracted to another electronegative atom from another polar molecule, such as water (H2O), hydrogen fluoride (HF), or ammonia (NH3). The huge electronegativity difference between the H atom (2.1) and the atom to which it is bonded (4.0 for an F atom, 3.5 for an O atom, or 3.0 for an N atom), combined with the very small size of an H atom...
Hydrogen Bonds
Hydrogen BondsHydrogen bonds are weak attractions between atoms that have formed other chemical bonds. One of these atoms is electronegative, like oxygen, and has a partial negative charge. The other is a hydrogen atom that has bonded with another electronegative atom and has a partial positive charge.Hydrogen Bonds Control the World!Because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom, such as oxygen or nitrogen, electrons in the bond are...

![Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F55858.jpg&w=3840&q=50)
