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首页> 外文期刊>Biochemistry >Resonance raman characterization of reaction centers with an Asp residue near the photoactive bacteriopheophytin
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Resonance raman characterization of reaction centers with an Asp residue near the photoactive bacteriopheophytin

机译：反应中心的共振拉曼光谱表征，其光敏噬菌素附近有一个Asp残基

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Q(y)-excitation resonance Raman (RR) studies are reported for a series of Rhodobacter capsulatus reaction centers (RCs) containing mutations at L-polypeptide residue 121 near the photoactive bacteriopheophytin (BPhL), The studies focus on the electronic/structural perturbations of BPhL induced by replacing the native Phe with an Asp residue. Earlier work has shown that the electron-transfer properties of F(L121)D RCs are closely related to those of RCs in which BPhL is replaced by bacteriochlorophyll (BChl) (beta-type RCs) or by pheophytin. In addition to the F(L121)D single mutant, RR studies were performed on the F(L121)D/E(L104)L double mutant, which additionally removes the hydrogen bond between BPhL and the native Glu L104 residue. The vibrational signatures of BPhL in the single and double mutants containing Asp L121 are compared with one another and with those of BPhL in both wild-type and F(L121)L RCs. The replacement of the aromatic Phe residue with Leu has no discernible effect on the vibrational properties of BPhL, a finding in concert with the previously reported absence of an effect of the mutation on the electron-transfer characteristics of the RC. In contrast, replacement of Phe with Asp significantly perturbs the vibrational characteristics of BPhL, and in a manner most consistent with Asp L121 being deprotonated and negatively charged. The negative charge of the carboxyl group of Asp L121 interacts with the pi-electron system of BPhL in a relatively nonspecific fashion, diminishing the contribution of charge-separated resonance forms of the C-9-keto group to the electronic structure of the cofactor. The presence of a negative charge near BPhL is consistent with the known photochemistry of F(L121)D RCs, which indicates that the free energy of P+BPhL- is substantially higher than in wild type RCs. [References: 42]
机译：Q（y）激发共振拉曼（RR）研究报道了一系列囊膜红球菌反应中心（RCs），其中在光敏噬菌体（BPhL）附近的L多肽残基121处含有突变，研究重点是电子/结构扰动通过用Asp残基取代天然Phe诱导的BPhL的表达。早期的工作表明，F（L121）D RCs的电子传递性质与其中BPhL被细菌叶绿素（BChl）（β型RCs）或脱镁叶绿素替代的RC的电子传递性质密切相关。除了F（L121）D单突变体，还对F（L121）D / E（L104）L双突变体进行了RR研究，该双突变体另外去除了BPhL和天然Glu L104残基之间的氢键。将含有Asp L121的单突变体和双重突变体中BPhL的振动特征相互比较，并与野生型和F（L121）L RCs中的BPhL振动特征相互比较。用Leu取代芳香族Phe残基对BPhL的振动性能没有明显影响，这一发现与先前报道的对RC的电子传输特性没有突变的影响相一致。相反，用Asp代替Phe会显着干扰BPhL的振动特性，并且最符合Asp L121被去质子化和带负电荷的方式。 Asp L121羧基的负电荷以相对非特异性的方式与BPhL的pi电子系统相互作用，从而减少了C-9-酮基的电荷分离共振形式对辅因子电子结构的贡献。 BPhL附近存在负电荷与F（L121）D RCs的已知光化学相符，这表明P + BPhL-的自由能明显高于野生型RCs。 [参考：42]

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