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首页> 外文期刊>Biochemistry >Charge Separation in Rhodobacter sphaeroides Mutant Reaction Centers with Increased Midpoint Potential of the Primary Electron Donor
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Charge Separation in Rhodobacter sphaeroides Mutant Reaction Centers with Increased Midpoint Potential of the Primary Electron Donor

机译：具有增加的初级电子给体中点电位的球形红球菌突变反应中心中的电荷分离

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Primary charge separation dynamics in four mutant reaction centers (RCs) of the purple bacterium Rhodobacter sphaeroides with increased midpoint potential of the primary electron donor P (M160LH, L131LH, M197FH, and M160LH + L131LH + M197FH) have been studied by femtosecond transient absorption spectroscopy at room temperature. The decay of the excited singlet state in the wild-type and mutant RCs is complex and has two main exponential components, which indicates heterogeneity of electron transfer rates or the presence of reverse electron transfer reactions. The radical anion band of monomeric bacteriochlorophyll B_A at 1020 nm was first observed in transient absorbance difference spectra of single mutants. This band remains visible, although with somewhat reduced amplitude, even at delays up to tens of picoseconds when stimulated emission is absent and the reaction centers are in the P~+H_A~- state. The presence of this band in this time period indicates the existence of thermodynamic equilibrium between the P~+B_A~-H_A and P~+B_AH_A~- states. The data give grounds for assuming that the value of the energy difference between the states P*, P~+B_A~-H_A, and P~+B_AH_A~- at early times is of the same order of magnitude as the energy kT at room temperature. Besides, monomeric bacteriochlorophyll B_A is found to be an immediate electron acceptor in the single mutant RCs, where electron transfer is hampered due to increased energy of the P~+B_A~-state with respect to P*.
机译：飞秒瞬态吸收光谱法研究了具有主电子供体P（M160LH，L131LH，M197FH和M160LH + L131LH + M197FH）的中点电势升高的紫色细菌球形变红细菌的四个突变反应中心（RCs）的主电荷分离动力学在室温下。野生型和突变型RC中激发单线态的衰减是复杂的，并且具有两个主要的指数成分，这表明电子传输速率的异质性或存在反向电子传输反应。首先在单个突变体的瞬时吸光度差光谱中观察到了单体细菌叶绿素B_A在1020 nm处的自由基阴离子带。该频带保持可见，尽管幅度有所减小，甚至在不存在受激发射且反应中心处于P〜+ H_A〜-状态时甚至长达数十皮秒的延迟时仍然可见。在该时间段中该带的存在表明P〜+ B_A〜-H_A和P〜+ B_AH_A〜-状态之间存在热力学平衡。数据为假设在早期时状态P *，P〜+ B_A〜-H_A和P〜+ B_AH_A〜-之间的能量差值与房间的能量kT处于相同数量级提供了依据温度。此外，单体细菌叶绿素B_A被发现是单个突变RCs中的直接电子受体，其中由于P〜+ B_A〜态相对于P *的能量增加，电子传递受到阻碍。

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