The pigment composition of isolated reaction centers (RCs) of the green filamentous bacterium Chloroflexus (Cfl.) aurantiacus was changed by chemical exchange of native bacteriopheophytin a (BPheo) molecules with externally added pheophytin a (Pheo) or [3-acetyl]-Pheo upon incubation of RC/pheophytin mixtures at room temperature and 45 °C. The modified RCs were characterized by Vis/NIR absorption spectroscopy, and the effect of pigment exchange on RC photochemical activity was assessed by measuring the photoaccumulation of the reduced pigment at the binding site H_A. It is shown that both pheophytins can be exchanged into the H_A site instead of BPheo by incubation at room temperature. While the newly introduced Pheo molecule is not active in electron transfer, the [3-acetyl]-Pheo molecule is able to replace functionally the photoreducible H_A BPheo molecule with the formation of the [3-acetyl]-Pheo⁻ radical anion instead of the BPheo⁻. After incubation at 45 °C, the majority (~ 90%) of H_A BPheo molecules is replaced by both Pheo and [3-acetyl]-Pheo. Only a partial replacement of inactive BPheo molecules with pheophytins is observed even when the incubation temperature is raised to 50 °C. The results are discussed in terms of (i) differences in the accessibility of BPheo binding sites for extraneous pigments depending on structural constraints and incubation temperature and (ii) the effect of the reduction potential of pigments introduced into the H_A site on the energetics of the charge separation process. The possible implication of Pheo-exchanged preparations for studying early electron-transfer events in Cfl. aurantiacus RCs is considered.

绿色丝状菌的分离反应中心（RCS）的颜料组合物Chloroflexus（CFL。 ）子囊菌被天然bacteriopheophytin的化学交换改变一个与外部加入的脱镁叶绿素（BPheo）分子一个（嗜铬细胞瘤）或[3-乙酰基] -Pheo在室温和 45°C 下孵育 RC/脱镁叶绿素混合物。修饰的 RCs 用 Vis/NIR 吸收光谱表征，并且通过测量结合位点 H _A处还原色素的光积累来评估色素交换对 RC 光化学活性的影响。结果表明，两种脱镁叶绿素都可以交换成 H _A通过在室温下孵育来代替 BPheo。虽然新引入的 Pheo 分子在电子转移中没有活性，但 [3-乙酰]-Pheo 分子能够在功能上取代可光还原的 H _A BPheo 分子，形成 [3-乙酰]-Pheo ^-自由基阴离子而不是BPheo ^-。在 45 °C 下孵育后，大部分 (~ 90%) H _ABPheo 分子被 Pheo 和 [3-乙酰]-Pheo 替代。即使将孵育温度提高到 50 °C，也只能观察到脱镁叶绿素部分替代了无活性的 BPheo 分子。结果根据 (i) BPheo 结合位点对外来色素的可及性的差异进行了讨论，具体取决于结构约束和孵育温度，以及 (ii) 引入 H _A位点的色素的还原电位对能量学的影响电荷分离过程。Pheo 交换制剂对研究Cfl 中早期电子转移事件的可能影响。aurantiacus RCs 被考虑。