Dynamics and energetics of cyanobacterial photosystem I:ferredoxin complexes in different redox states
Dynamics and energetics of cyanobacterial photosystem I:ferredoxin complexes in different redox states
复制标题
蓝藻光系统I：不同氧化还原态铁氧化还原蛋白复合物的动力学和能量学
DOI：
10.1016/j.bbabio.2017.04.001
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Kurisu Genji
中科院分区：
文献类型：
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作者：
Setif Pierre;Mutoh Risa;Kurisu Genji
光系统-I/PSI还原铁氧还蛋白/Fd的快速周转要求它在被PSI：Fd复合体内电子转移还原后迅速解离。用闪光吸收光谱测定了蓝藻PSI和FDS的不同组合以及FD和末端PSI受体(FAFB)的不同氧化还原状态下FD从PSI中解离的速率常数。新获得的数值首先来自于PSI和氧化还原失活的镓取代的FD之间的离解常数随着(FAFB)还原而增加的事实，其次来自对复合体内FD还原到氧化的FD与PSI结合的动力学相的描述和解释，该过程受还原的FD与PSI的上述解离的速度限制。以含氧化配对的络合物为参照，离解速率常数随(FAFB)的单次还原而适度增大，电子从(FAFB)−向FD转移后，解离速率常数增加约一个数量级，有利于FD被PSI还原。以加长热核球菌为配对，测定了S−1的氧化还原、还原还原和还原还原的−-GT_1分别为270、730和10000。此外，假设还原的FD和PSI之间的结合速率常数有一个保守的上限，则计算出与PSI结合时FD中点电位的显著负移(<；−60 mV对于长链热球菌属)。从目前的知识状态来看，问题仍然是悬而未决的，即这种氧化还原位移是否与从(FAFB)−中还原FD的一个大的(>10)平衡常数兼容。
Fast turnover of ferredoxin/Fd reduction by photosystem-I/PSI requires that it dissociates rapidly after it has been reduced by PSI:Fd intracomplex electron transfer. The rate constants of Fd dissociation from PSI have been determined by flash-absorption spectroscopy with different combinations of cyanobacterial PSIs and Fds, and different redox states of Fd and of the terminal PSI acceptor (FAFB). Newly obtained values were derived firstly from the fact that the dissociation constant between PSI and redox-inactive gallium-substituted Fd increases upon (FAFB) reduction and secondly from the characterization and elucidation of a kinetic phase following intracomplex Fd reduction to binding of oxidized Fd to PSI, a process which is rate-limited by the foregoing dissociation of reduced Fd from PSI. By reference to the complex with oxidized partners, dissociation rate constants were found to increase moderately with (FAFB) single reduction and by about one order of magnitude after electron transfer from (FAFB)−to Fd, therefore favoring turnover of Fd reduction by PSI. WithThermosynechococcus elongatuspartners, values of 270, 730 and > 10000 s−1were thus determined for (FAFB)Fdoxidized, (FAFB)−Fdoxidizedand (FAFB)Fdreduced, respectively. Moreover, assuming a conservative upper limit for the association rate constant between reduced Fd and PSI, a significant negative shift of the Fd midpoint potential upon binding to PSI has been calculated (< −60 mV forThermosynechococcus elongatus). From the present state of knowledge, the question is still open whether this redox shift is compatible with a large (> 10) equilibrium constant for intracomplex reduction of Fd from (FAFB)−.