Primary donor recovery kinetics in reaction centers from Rhodopseudomonas viridis. The influence of ferricyanide as a rapid oxidant of the acceptor quinones.
Primary donor recovery kinetics in reaction centers from Rhodopseudomonas viridis. The influence of ferricyanide as a rapid oxidant of the acceptor quinones.
复制标题
绿色红假单胞菌反应中心的主要供体回收动力学。
DOI：
10.1016/0005-2728(86)90212-4
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发表时间：
1986
期刊：
影响因子：
--
通讯作者：
Wraight,CA
中科院分区：
文献类型：
--
作者：
Shopes,RJ;Wraight,CA
在含有单一醌的绿红假单胞菌的反应中心，当结合的供体细胞色素被铁氰化物化学氧化时，发现光氧化的主要供体P+的衰变是双相的。两相的比例与pH有关，表观pK为7.6。一个快速相，在pH值为9.5时占主导地位（t 12 = 1 ms），与P+和主受体Q−A的预期电荷重组相对应。一个慢得多的相，在低pH时占主导地位，被证明是由铁氰化物在Q−A被铁氰化物快速氧化的反应中心缓慢还原P+引起的。Q−A氧化速率与铁氰化物活性呈线性关系，且与ph值密切相关。二阶速率常数经铁氰化物活度系数校正后，在低pH条件下达到最大值2·10 8 M−1·s−1，但随着pH高于ap K 5.8而逐渐减小，表明反应中心处于质子化状态。亚铁氰化物对P+的缓慢还原也是二阶的，在低pH下的最大还原速率常数为8·10.5 M−1·s−1，校正了亚铁氰化物的活度系数。该速率在较高的pH下也降低，ap K为7.4，表明亚铁氰化物也以质子化形式反应中心最活跃。铁氰化物对Q−A的氧化不受邻菲罗啉存在的影响，这意味着对Q−A的获取不是通过Q b结合位点。在补充了泛醌的反应中心，观察到还原的仲醌Q−B被铁氰化物氧化，但比Q−A的氧化速度要慢得多。这表明Q−B可能通过Q−A被氧化，因此速度由Q−A Q B a3 Q A Q−B的平衡常数调节。
In reaction centers from Rhodopseudomonas viridis that contain a single quinone, the decay of the photo-oxidized primary donor, P+, was found to be biphasic when the bound, donor cytochromes were chemically oxidized by ferricyanide. The ratio of the two phases was dependent on pH with an apparent pK of 7.6. A fast phase, which dominated at high pH (t 1 2= 1 ms at pH 9.5), corresponded to the expected charge recombination of P+ and the primary acceptor Q− A. A much slower phase dominated at low pH and was shown to arise from a slow reduction of P+ by ferrocyanide in reaction centers where Q− A has been rapidly oxidized by ferricyanide. The rate of Q− A oxidation was linear with respect to ferricyanide activity and was strongly pH-dependent. The second-order rate constant, corrected for the activity coefficient of ferricyanide, approached a maximum of 2· 10 8 M− 1· s− 1 at low pH, but decreased steadily as the pH was raised above ap K of 5.8, indicating that a protonated state of the reaction center was involved. The slow reduction of P+ by ferrocyanide was also second-order, with a maximum rate constant at low pH of 8· 10 5 M− 1· s− 1 corrected for the activity coefficient of ferrocyanide. This rate also decreased at higher pH, with ap K of 7.4, indicating that ferrocyanide also was most reactive with a protonated form of the reaction center. The oxidation of Q− A by ferricyanide was unaffected by the presence of o-phenanthroline, implying that access to Q− A was not via the Q B-binding site. In reaction centers supplemented with ubiquinone, oxidation of reduced secondary quinone, Q− B, by ferricyanide was observed but was substantially slower than that for Q− A. It is suggested that Q− B may be oxidized via Q A so that the rate is modulated by the equilibrium constant for Q− A Q B a3 Q A Q− B.