大豆リポキシゲネーゼにおけるプロトン結合電子移転:動的同位体効果のダイナミックな行動と温度依存性
Elizabeth Hatcher1, Alexander V Soudackov, Sharon Hammes-Schiffer
1Department of Chemistry, 104 Chemistry Building, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Journal of the American Chemical Society
|January 4, 2007
まとめ
この研究は,量子力学的効果とタンパク質の動きが,大豆リポキシゲネーゼの運動同位体効果を支配することを明らかにしています. トンネリングと振動の重なりは,実験データに適合することなく,観察された効果を説明します.
科学分野:
- バイオケミストリー バイオケミストリー
- 化学物理 化学物理
- エンジム・キネティクス
背景:
- 大豆のリポキシゲネーゼは,陽子結合電子伝送反応を触媒化する.
- 動的同位体効果 (KIEs) の動的行動と温度依存性の理解は,酵素機構の解明に極めて重要です.
研究 の 目的:
- 大豆リポキシゲナーゼ反応におけるKIEsのダイナミックな行動と温度依存性を調査する.
- 反応機構における量子力学的効果,タンパク質の運動,陽子伝達ダイナミクスの役割を明らかにする.
主な方法:
- 電子と陽子の量子力学を組み込んだ振動的に非アディアバティックな配列を採用した.
- 溶解酵素システム全体について,古典的な分子ダイナミクスシミュレーションを用いた.
- 振動的結合とエネルギーギャップのダイナミクスに依存する確率フクロス相関関数を用いて計算された速度定数.
主要な成果:
- 確率フクロス相関関数の動的行動は,主にタンパク質と溶媒の動きによって引き起こされます.
- 全体的な反応速度は,陽子ドナー-受容体の周波数,ビブロン結合,再構成エネルギーによって大きく影響を受けます.
- 計算は,パラメータのフィッティングなしで,実験的なKIEの大きさと温度依存を正確に再現しました.
結論:
- 地下振動的状態と振動波関数の重複の間の量子力学的トンネリングは,大きなKIEの大きさの鍵です.
- KIEの弱い温度依存は,地元の陽子ドナー-受容体運動の優位性によるものである.
- この研究は,酵素触媒による陽子結合電子移転反応を理解するための詳細な理論的枠組みを提供します.
関連する概念動画
02:39Phase Transitions: Melting and Freezing
Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
02:55Temperature Dependence on Reaction Rate
The Collision Theory
Atoms, molecules, or ions must collide before they can react with each other. Atoms must be close together to form chemical bonds. This premise is the basis for a theory that explains many observations regarding chemical kinetics, including factors affecting reaction rates.
The collision theory is based on the postulates that (i) the reaction rate is proportional to the rate of reactant collisions, (ii) the reacting species collide in an orientation allowing contact between...
Atoms, molecules, or ions must collide before they can react with each other. Atoms must be close together to form chemical bonds. This premise is the basis for a theory that explains many observations regarding chemical kinetics, including factors affecting reaction rates.
The collision theory is based on the postulates that (i) the reaction rate is proportional to the rate of reactant collisions, (ii) the reacting species collide in an orientation allowing contact between...
02:11Effects of Temperature on Free Energy
The spontaneity of a process depends upon the temperature of the system. Phase transitions, for example, will proceed spontaneously in one direction or the other depending upon the temperature of the substance in question. Likewise, some chemical reactions can also exhibit temperature-dependent spontaneities. To illustrate this concept, the equation relating free energy change to the enthalpy and entropy changes for the process is considered:
02:28Effect of Temperature Change on Reaction Rate
The Arrhenius equation,
01:13Introduction to Mechanisms of Enzyme Catalysis
For many years, scientists thought that enzyme-substrate binding took place in a simple "lock-and-key" fashion. This model stated that the enzyme and substrate fit together perfectly in one instantaneous step. However, current research supports a more refined view scientists call induced fit. The induced-fit model expands upon the lock-and-key model by describing a more dynamic interaction between enzyme and substrate. As the enzyme and substrate come together, their interaction causes a mild...
01:25Transition State Theory
Transition-state theory, also known as activated-complex theory, provides a molecular-level explanation of reaction rates in both gas-phase and solution-phase reactions. It extends earlier kinetic models by considering the formation of a short-lived, high-energy configuration during a reaction.The progress of a chemical reaction can be represented using a reaction profile, which plots potential energy against the reaction coordinate. As two reactant molecules approach one another, their...