Probing the coupling between proton and electron transfer in photosystem II core complexes containing a 3-fluorotyrosine.
Probing the coupling between proton and electron transfer in photosystem II core complexes containing a 3-fluorotyrosine.
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DOI：
10.1021/ja808604h
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发表时间：
2009-04-01
影响因子：
15
通讯作者：
Diner BA
中科院分区：
文献类型：
--
作者：
Rappaport F;Boussac A;Force DA;Peloquin J;Brynda M;Sugiura M;Un S;Britt RD;Diner BA
许多酶的催化循环涉及质子转移和电子转移之间的耦合。然而，对生物系统中这种协调转移的理解仍然有限，可能是因为其表征依赖于与电子或质子转移相关的自由能变化的受控但具有实验挑战性的修改。我们在光系统II中进行了这样的研究。通过改变P680的轴向配体，使TyrZ与P680·+之间的电子转移驱动力降低了约80 meV;通过用3-氟酪氨酸（3F-TyrZ）取代TyrZ，使TyrZ氧化后的质子转移驱动力降低了约80 meV。在Mn耗尽的光系统II中，TyrZ和3F-TyrZ的氧化速率对pH的依赖性被发现是相似的。然而，在TyrZ的酚羟基参与与质子受体的H-键的pH范围内，3F-TyrZ的氧化活化能降低110 meV，该值与体外发现的与Tyr相比时3F-Tyr的酚盐形式的90 meV稳定化能相关（Seyedsayamdost等人，2006，JACS 128：1569-79）。因此，当YZ的苯酚作为氢键供体时，其被P680·+氧化是由其先前的去质子化控制的。这与较低pH下的情况形成对比，在较低pH下，质子受体被质子化，因此不可用，其中氧化诱导的TyrZ酚羟基质子转移与电子转移到P680·+一致。这表明在pH7.5的协同质子/电子转移之间的切换< 7.5 to a sequential one at pHs >，并说明了氢键和酚盐与附近质子受体之间存在的可能的盐桥在确定质子和电子转移之间的耦合中的作用。
The catalytic cycle of numerous enzymes involves the coupling between proton transfer and electron transfer. Yet, the understanding of this coordinated transfer in biological systems remains limited, likely because its characterization relies on the controlled but experimentally challenging modifications of the free energy changes associated with either the electron or proton transfer. We have performed such a study here in Photosystem II. The driving force for electron transfer from TyrZ to P680•+ has been decreased by ~ 80 meV by mutating the axial ligand of P680, and that for proton transfer upon oxidation of TyrZ by substituting a 3-fluorotyrosine (3F-TyrZ) for TyrZ. In Mn-depleted Photosystem II, the dependence upon pH of the oxidation rates of TyrZ and 3F-TyrZ were found to be similar. However, in the pH range where the phenolic hydroxyl of TyrZ is involved in a H-bond with a proton acceptor, the activation energy of the oxidation of 3F-TyrZ is decreased by 110 meV, a value which correlates with the in vitro finding of a 90 meV stabilization energy to the phenolate form of 3F-Tyr when compared to Tyr (Seyedsayamdost et al., 2006, JACS 128:1569–79). Thus, when the phenol of YZ acts as a H-bond-donor, its oxidation by P680•+ is controlled by its prior deprotonation. This contrasts with the situation prevailing at lower pH, where the proton acceptor is protonated and therefore unavailable, in which the oxidation-induced proton transfer from the phenolic hydroxyl of TyrZ has been proposed to occur concertedly with the electron transfer to P680•+. This suggests a switch between a concerted proton/electron transfer at pHs < 7.5 to a sequential one at pHs > 7.5 and illustrates the roles of the H-bond and of the likely salt-bridge existing between the phenolate and the nearby proton acceptor in determining the coupling between proton and electron transfer.
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DOI：
10.1016/0005-2728(84)90256-1
发表时间：
1984-01-01
期刊：
BIOCHIMICA ET BIOPHYSICA ACTA
影响因子：
--
作者：
BRETTEL, K;SCHLODDER, E;WITT, HT
通讯作者：
WITT, HT
影响因子：
15
作者：
Irebo, Tania;Reece, Steven Y.;Hammarstrom, Leif
通讯作者：
Hammarstrom, Leif
影响因子：
3.3
作者：
Diner, BA;Bautista, JA;Chisholm, DA
通讯作者：
Chisholm, DA
影响因子：
3.5
作者：
ECKERT, HJ;RENGER, G
通讯作者：
RENGER, G
影响因子：
4.3
作者：
Grabolle, M;Dau, H
通讯作者：
Dau, H