フォトシステムIIの核複合体において,3-フローロチロシンを含む核複合体において,陽子と電子の移転の間の結合を調査した
Fabrice Rappaport1, Alain Boussac, Dee Ann Force
1Institut de Biologie Physico-Chimique, UMR 7141 CNRS-UPMC, 13 rue Pierre et Marie Curie, 75005 Paris, France. Fabrice.Rappaport@ibpc.fr
Journal of the American Chemical Society
|March 7, 2009
まとめ
フォトシステムIIにおける陽子と電子の移動は,pHに応じて協調的なメカニズムから連続的なメカニズムに切り替わります. このpH依存のスイッチは,Tyr (Z) 酸化で観察され,結合された電子-陽子移転を調節する際に,水素結合と塩橋の役割を強調しています.
科学分野:
- バイオケミストリー バイオケミストリー
- 光合成に関する研究.
- 酵素触媒は,酵素を触媒として用いる.
背景:
- 酵素触媒はしばしば陽子と電子の移転を組み合わせる.
- この結合の特徴付けは,自由エネルギーの変化を実験的に修正する難しさのために困難です.
- 光学系IIは,これらの結合移転を研究するための重要な生物学的システムです.
研究 の 目的:
- フォトシステムIIにおける協調された陽子と電子の移転メカニズムを調査する.
- Tyr(Z) からP(680)(*+) への電子移転の調節におけるpHと水素結合の役割を明らかにする.
主な方法:
- 電子移転の原動力を変化させるための光システムIIの変異 (軸性リガンド変異).
- Tyr (Z) に対して,3-fluorotyrosine (3F-Tyr (Z)) の置換により,陽子の転移エネルギーが変化する.
- 酸化率のTyr (Z) と3F-Tyr (Z) のpHに依存した動力学的研究が,Mn欠乏した光システムIIで実施された.
主要な成果:
- Tyr (Z) と3F-Tyr (Z) の酸化速度は,同様のpH依存性を示した.
- 水素結合の存在で,3F-Tyr (Z) 酸化の活性化エネルギーは110 meV減少した.
- この減少は,3F-Tyrフェノラート形態の90 meVの安定化と相関していた.
結論:
- より高いpH (>7.5) で,Tyr (Z) の酸化は先行的な脱プロトン化によって制御され,連続的な陽子-電子の移転を示します.
- 低 pH (<7.5) では,Tyr (Z) からの陽子の移転は,電子の移転と協調して起こります.
- 水素結合と塩の架け橋は,光学系IIにおける陽子と電子の移動の結合機構を決定する上で重要な役割を果たします.
関連する概念動画
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