Coordination of proton and electron transfer from the redox-active tyrosine, YZ, of Photosystem II and examination of the electrostatic influence of oxidized tyrosine, YD•(H+)
Coordination of proton and electron transfer from the redox-active tyrosine, YZ, of Photosystem II and examination of the electrostatic influence of oxidized tyrosine, YD•(H+)
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DOI：
10.1039/b407423h
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发表时间：
2004-01-01
影响因子：
3.3
通讯作者：
Chisholm, DA
中科院分区：
文献类型：
--
作者：
Diner, BA;Bautista, JA;Chisholm, DA
光系统 II 的氧化还原活性酪氨酸 Y-Z 和 Y-D 被 P-680(+) 氧化成中性自由基。这种氧化需要将电子转移与酚质子的转移耦合。对贫锰 PSII 核心复合物中 Y-Z 氧化多相动力学的研究表明，动力学成分的相对振幅与 pH 相关，其中一个成分在微秒至数十微秒范围内 (pH 4-8) 显示出 pH 依赖性 t(1/2)。 Sjodin 及其同事（M. Sjodin、S. Styring、B. Angstromkemark、L. Sun 和 L. Hammarstrom、Philos. Trans. R. Soc. London, Ser. B, 2002, 357, 1471-1479）表明，后一种组分的速率随 pH 值的增加反映了通过降低还原电位来增加反应驱动力。 Y-Z(.)/Y-Z，与电子和质子协同转移（CEP机制）一致。这里通过修改 P-680(+)/P-680 的还原电位，即不修改质子受体或质子转移途径，报告了 Y-Z 氧化速率对 DeltaG 度的类似依赖性。这里报道的结果支持 CEP 机制，尽管不能完全排除酪氨酸盐的形成和随后的电子转移。氧化酪氨酸 Y-D(.)(H+) 的存在已被证明可以加速放氧复合物的光活化，这可能是通过增加 P-680(+)/P-680 的还原电位来实现的。此处通过测量 WT 菌株和集胞藻 6803 无 Y-D 菌株的贫锰核心复合物中 Y-Z 氧化速率，检查 Y-D(.) (H+) 对 P-680(+)/P-680 还原电位的影响。还检查了 Y-D(.) (H+) 对 P-680(+)-P-680 差异谱的影响。这些比较表明Y-D(.)(H+)对氧化还原对P-680(+)/P-680还原电位的静电贡献非常小(小于或等于10 mV)，这意味着Y-D(.)(H+)在光活化中的作用可能更多地与其在锰簇组装过程中提供氧化当量有关。
The redox active tyrosines, Y-Z and Y-D, of Photosystem II are oxidized by P-680(+) to the neutral radical. Such oxidation requires coupling of electron transfer to the transfer of the phenolic proton. Studies of the multiphasic kinetics of Y-Z oxidation in Mn-depleted PSII core complexes have shown that the relative amplitudes of the kinetic components are pH-dependent with one component showing a pH-dependent t(1/2) in the microsecond to tens of microsecond range (pH 4-8). Sjodin and coworkers (M. Sjodin, S. Styring, B. Angstromkemark, L. Sun and L. Hammarstrom, Philos. Trans. R. Soc. London, Ser. B, 2002, 357, 1471-1479) have suggested that the increase in rate of this latter component with pH reflects an increase in the driving force of the reaction by lowering the reduction potential of Y-Z(.)/Y-Z, consistent with concerted electron and proton transfer (CEP mechanism). A similar dependence of the rate of Y-Z oxidation on DeltaGdegrees is reported here through modification of the reduction potential of P-680(+)/P-680, that is, without modifying either the proton acceptor or the pathway for proton transfer. The results reported here support a CEP mechanism, though formation of the tyrosinate followed by electron transfer cannot be completely ruled out. The presence of oxidized tyrosine Y-D(.)(H+) has been shown to accelerate the photoactivation of the oxygen evolving complex, possibly by an increase in the reduction potential of P-680(+)/P-680. The influence of Y-D(.) (H+) on the P-680(+)/P-680 reduction potential is examined here by measuring the rate of Y-Z oxidation in Mn-depleted core complexes from the WT strain and from a Y-D-less strain of Synechocystis 6803. Also examined is the influence of Y-D(.) (H+) on the P-680(+)-P-680 difference spectrum. These comparisons show that the electrostatic contribution of Y-D(.)(H+) to the reduction potential of redox couple P-680(+)/P-680 is very small (less than or equal to10 mV), implying that the role of Y-D(.)(H+) in photoactivation may have more to do with its providing an oxidizing equivalent during assembly of the manganese cluster.