フラボ酵素 TrmFO の TyrOH•+ ラジカルカチオンの識別
Lipsa Nag1, Pierre Sournia1, Hannu Myllykallio1
1LOB, Ecole Polytechnique, CNRS, INSERM, Université Paris-Saclay , Palaiseau 91128 Cedex, France.
Journal of the American Chemical Society
|July 27, 2017
まとめ
研究者らは,生化学反応における重要な中間物質であるプロトン化チロシル基 (TyrOH•+) を特定した. この発見は,電荷移転プロセスとフラボタンパク質の光化学を理解するのに役立ちます.
科学分野:
- 生物化学
- バイオ物理学
- スペクトロスコーピー
背景:
- タイロシン (TyrOH) とトリプトファンラジカルは,生物学的電荷移転反応における重要な中間物質である.
- トリプトファニルラジカルは,陽子化と中性的な形態で存在しますが,チロシルラジカルは中性的で陽子化されていない状態でのみ観察されています.
- 複雑な生化学的経路を解明する鍵となるのです
研究 の 目的:
- フラボ酵素モデルシステムを用いて,陽子化されたチロシル基 (TyrOH•+) を特徴づける.
- TyrOH•+のスペクトルおよび時間的性質を調査する.
- TyrOHの酸化と脱プロトンの関係を明らかにする.
主な方法:
- 遺伝子組み換えフラボ酵素を モデルシステムとして使った
- 超高速光と吸収スペクトロスコーピーを使った.
- 陽子化されたチロシル基の形成と分解の動態を分析した.
主要な成果:
- 陽子化されたチロシル基 (TyrOH•+) を特徴付け,明確な可視吸収帯を観察した.
- TyrOH•+の移行モメントはフェノルの対称性軸の近くにあると決定した.
- 電子移転により1ps以内のTyrOH•+形成と3ps以内の電荷再結合による崩壊を示した.
結論:
- 陽子化されたチロシル基 (TyrOH•+) は,異なるスペクトルおよび時間的性質を有する.
- TyrOHの酸化は必ずしも即時の脱プロトン化につながらない.
- これらの発見は,フラボタンパク質の光産物状態を区別し,チロシル中間物質を含む酸化還元連鎖を理解するのに役立ちます.
関連する概念動画
Aromatic Hydrocarbon Cations: Structural Overview
4.0K
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group...
Removing one hydrogen from the intervening CH2 group...
4.0K
Keto–Enol Tautomerism: Mechanism
8.0K
The keto and enol forms are known as tautomers and they constantly interconvert (or tautomerize) between the two forms under acid or base catalyzed conditions. Both the reactions involve the same steps—protonation and deprotonation— although in the reverse order.
8.0K
Radicals: Electronic Structure and Geometry
5.3K
This lesson delves into the geometry of a radical, which is influenced by the electronic structure of the molecule. The principle is similar to that of a lone pair, where the unpaired electron influences the geometry at the radical center.
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...
5.3K
Thermal and Photochemical Electrocyclic Reactions: Overview
3.1K
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
3.1K
Radical Autoxidation
3.3K
The oxidation of an organic compound in the presence of air or oxygen is called autoxidation. For example, cumene reacts with oxygen to form hydroperoxide. Autoxidation involves initiation, propagation, and termination steps. Many organic compounds are susceptible to autoxidation—especially ethers in the presence of oxygen, which form hydroperoxides. Even though this reaction is slow, old ether bottles contain small amounts of peroxide, which leads to laboratory explosions during ether...
3.3K
Radical Reactivity: Overview
2.8K
Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
2.8K


