探测光系统II核心复合体中的质子和电子转移之间的合,这些复合体中含有3-甲
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
概括
光系统II中的质子和电子转移,根据pH值,从协同转换为顺序转换. 在Tyr(Z) 氧化中观察到的这种依赖pH的开关,突出了键和盐桥在调节合电子-质子转移中的作用.
科学领域:
- 生物化学 生物化学
- 光合作用研究研究光合作用.
- 酶催化酶的催化作用
背景情况:
- 酶催化通常将质子和电子转移结合起来.
- 鉴定这种合是具有挑战性的,因为很难在实验中修改自由能量变化.
- 光系统II是研究这些合转移的关键生物系统.
研究的目的:
- 调查光系统II中协调的质子和电子转移机制.
- 阐明pH和键在调节Tyr(Z) 到P(680)(*+) 电子转移中的作用.
主要方法:
- 光系统II的突变发生以改变电子转移的驱动力 (轴联体突变).
- 替代Tyr(Z) 的3 - 托洛辛 (3F-Tyr(Z)) 来修改质子转移能量.
- 在缺乏Mn的光系统II中对Tyr (Z) 和3F-Tyr (Z) 的氧化速率进行了pH依赖的动力学研究.
主要成果:
- Tyr (Z) 和3F-Tyr (Z) 的氧化速率显示出类似的pH依赖.
- 在存在键的情况下,3F-Tyr (Z) 氧化激活能量减少了110 meV.
- 这种降低与3F-Tyr酸形式的90 meV稳定相关.
结论:
- 在更高的pH值 (>7.5) 时,Tyr (Z) 氧化通过先前的去质子化控制,表明了顺序的质子-电子转移.
- 在较低的pH值 (<7.5) 时,来自Tyr的质子转移与电子转移一致发生.
- 键和盐桥在确定光系统II中质子和电子转移之间的合机制方面发挥着至关重要的作用.
相关概念视频
01:27Photosystem I
Although structurally similar to photosystem II (PSII), photosystem I (PSI) is has a different electron supplier and electron acceptor.
Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...
Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...
01:22Photosystem II
The multi-protein complex photosystem II (PS II) harvests photons and transfers their energy through its bound pigments to its reaction center, and ultimately to photosystem I (PSI) through the electron transport chain. The pigments responsible for caputirng the light energy in photosystems include chlorophyll a, chlorophyll b, and carotenoids.
The pigment molecules are arranged across two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
The pigment molecules are arranged across two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
01:29The Photochemical Reaction Center
Reaction centers are pigment-protein complexes that initiate energy conversion from photons to chemical entities. Therefore, photochemical reaction center is a more appropriate term that describes these complexes. The Nobel laureates Robert Emerson and William Arnold provided the first experimental evidence of photochemical reaction centers by demonstrating the participation of nearly 2,500 chlorophyll molecules for the release of just one molecule of oxygen. Despite thousands of photosynthetic...
01:32Photosystems
Photosystems are multiprotein complexes that form the functional units of photosynthesis in plants, algae, and cyanobacteria. They are found embedded in the membrane of tiny sac-like structures called thylakoids placed inside the chloroplast.
Functioning of Photosystems
Photosystems contain many pigment molecules, such as chlorophylls and carotenoids, arranged in a particular organization across two domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
Functioning of Photosystems
Photosystems contain many pigment molecules, such as chlorophylls and carotenoids, arranged in a particular organization across two domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
01:34The Z-Scheme of Electron Transport in Photosynthesis
The light reactions of photosynthesis assume a linear flow of electrons from water to NADP+. During this process, light energy drives the splitting of water molecules to produce oxygen. However, oxidation of water molecules is a thermodynamically unfavorable reaction and requires a strong oxidizing agent. This is accomplished by the first product of light reactions: oxidized P680 (or P680+), the most powerful oxidizing agent known in biology. The oxidized P680 that acquires an electron from the...
01:43Electron Transport Chain: Complex III and IV
During the electron transport chain, electrons from NADH and FADH2 are first transferred to complexes I and II, respectively. These two complexes then transfer the electrons to ubiquinol, which carries them further to complex III. Complex III passes the electrons across the intermembrane space to Cyt c, which carries them further to complex IV. Complex IV donates electrons to oxygen and reduces it to water. As electrons pass through complexes I, III, and IV, the energy released aids the pumping...