Gallium ferredoxin as a tool to study the effects of ferredoxin binding to photosystem I without ferredoxin reduction
Gallium ferredoxin as a tool to study the effects of ferredoxin binding to photosystem I without ferredoxin reduction
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DOI：
10.1007/s11120-016-0332-0
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发表时间：
2017-12-01
影响因子：
3.7
通讯作者：
Setif, Pierre
中科院分区：
文献类型：
--
作者：
Mignee, Clara;Mutoh, Risa;Setif, Pierre
光系统I（PSI）对铁氧还蛋白的还原涉及PsaC所含的[4Fe-4S]团簇F-A和F-B，其中F-B是铁氧还蛋白（Fd）的直接电子传递伙伴。通过闪光吸收光谱研究氧化还原非活性镓铁氧还蛋白与PSI的结合，研究P700（+）衰变和在Fd（Ga）存在下天然铁Fd的还原。Fd（Ga）结合导致P700（+）和（F-A，F-B）（-）之间更快的重组，（F-A，F-B）（-）向外源受体的电子逃逸更慢，复合物内Fd（Fe）还原量减少，这与Fd（Fe）和Fd（Ga）之间的竞争性结合一致。[Fd（Ga）]滴定这些效应表明，PSI：Fd（Ga）络合物的解离常数是不同的，无论（F-A，F-B）是氧化还是单独还原。这种结合的差异以及重组率的增加都可以归因于c。由于Fd（Ga）结合，（F-A，F-B）（被视为单电子受体）的中点电位发生-30 mV偏移。Fd（Ga）结合的这种效应，由于两种Fd的高度相似的结构和相同的电荷，可以外推到Fd（Fe），应该有助于PSI：Fd络合物内电子转移的不可逆性。还讨论了Fd结合对F-A和F-B的个体中点电位的影响，以及对PSI内电子转移和逃逸过程的可能后果。
Reduction of ferredoxin by photosystem I (PSI) involves the [4Fe-4S] clusters F-A and F-B harbored by PsaC, with F-B being the direct electron transfer partner of ferredoxin (Fd). Binding of the redox-inactive gallium ferredoxin to PSI was investigated by flash-absorption spectroscopy, studying both the P700(+) decay and the reduction of the native iron Fd in the presence of Fd(Ga). Fd(Ga) binding resulted in a faster recombination between P700(+) and (F-A, F-B)(-), a slower electron escape from (F-A, F-B)(-) to exogenous acceptors, and a decreased amount of intracomplex Fd(Fe) reduction, in accordance with competitive binding between Fd(Fe) and Fd(Ga). [Fd(Ga)] titrations of these effects revealed that the dissociation constant for the PSI:Fd(Ga) complex is different whether (F-A, F-B) is oxidized or singly reduced. This difference in binding, together with the increase in the recombination rate, could both be attributed to a c. -30 mV shift of the midpoint potential of (F-A, F-B), considered as a single electron acceptor, due to Fd(Ga) binding. This effect of Fd(Ga) binding, which can be extrapolated to Fd(Fe) because of the highly similar structure and the identical charge of the two Fds, should help irreversibility of electron transfer within the PSI:Fd complex. The effect of Fd binding on the individual midpoint potentials of F-A and F-B is also discussed with respect to the possible consequences on intra-PSI electron transfer and on the escape process.