Antenna excited state decay kinetics establish primary electron transfer in reaction centers as heterogeneous.
Antenna excited state decay kinetics establish primary electron transfer in reaction centers as heterogeneous.
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天线激发态衰变动力学将反应中心的初级电子转移确定为异质的。
DOI：
10.1021/bi970672a
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
Pearlstein,RM
中科院分区：
文献类型：
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作者：
Laible,PD;Greenfield,SR;Wasielewski,MR;Hansen,DK;Pearlstein,RM
已观察到细菌光合反应中心（膜结合和洗涤剂隔离）中激发的初级电子供体P* 的衰减在几十皮秒的时间尺度上是非指数的。虽然P* 的多皮秒非指数性被归因于初级电子转移（PET）速率的不均匀性，但衰变动力学也可以用均匀模型来解释。为了解决这种模糊性，我们研究了衰减的激发细菌叶绿素（Bchl）在膜结合的核心天线/反应中心复合物的野生型和突变体反应中心菌株ofRhodobacter capsulatus。从这些相同的菌株分离的反应中心显示一系列的多指数在初级电荷分离。突变菌株携带位于反应中心的活性和/或非活性侧上的单体Bchl附近的氨基酸的取代。监测天线Bchls的Qybleach的瞬态吸收测量需要至少两个指数分量来拟合所有衰减。野生型与等振幅组件，其寿命为24和65 ps。最短寿命的组分对突变相对不敏感，而较长寿命的组分的振幅和幅度受到氨基酸取代的显著干扰。与孤立的反应中心的情况不同，这里唯一的动力学模型与数据一致的是那些在其中的主要电子转移速率常数是异质的，这表明至少有两个结构群体的RC。在具有最短寿命天线衰减的群体中的PET导致动力学是转移到陷阱限制的，而在具有较长寿命天线衰减的其他群体中的动力学受到PET速率的限制。在一个单一的捕光系统中观察到这两种类型的动力学限制是出乎意料的，并且使光合作用中光能利用的限速步骤的任何讨论变得复杂。
The decay of the excited primary electron donor P* in bacterial photosynthetic reaction centers (both membrane-bound and detergent-isolated) has been observed to be nonexponential on a time scale of some tens of picoseconds. Although the multipicosecond nonexponentiality of P* has been ascribed to heterogeneity in the rate of primary electron transfer (PET), the decay kinetics can be interpreted equally well using homogeneous models. To address this ambiguity, we studied the decay of excited bacteriochlorophyll (Bchl) in the membrane-bound core antenna/reaction center complexes of wild-type and mutant reaction center strains ofRhodobacter capsulatus. Reaction centers isolated from these same strains display a range of multiexponentiality in primary charge separation. The mutant strains carry substitutions of amino acids residing near the monomeric Bchl on the active and/or inactive sides of the reaction center. Transient absorption measurements monitoring the Qybleach of antenna Bchls require at least two exponential components to fit all decays. The wild type was fitted with equal-amplitude components whose lifetimes are 24 and 65 ps. The shortest-lived component is relatively insensitive to mutation, in contrast to the longer-lived component(s) whose amplitude and magnitude were dramatically perturbed by amino acid substitutions. Unlike the situation with isolated reaction centers, here the only kinetic models consistent with the data are those in which the primary electron-transfer rate constant is heterogeneous, suggesting at least two structural populations of RCs. PET in the population with the shortest-lived antenna decay causes the kinetics to be transfer-to-trap-limited, whereas the kinetics in the other population(s)having longer-lived antenna decaysare limited by the rate of PET. Observation of both types of kinetic limitation within a single light-harvesting system is unexpected and complicates any discussion of the rate-limiting step of light energy utilization in photosynthesis.