The core light-harvesting complexes (LH1) in bacteriochlorophyll (BChl) b-containing purple phototrophic bacteria are characterized by a near-infrared absorption maximum around 1010 nm. The determinative cause for this ultra-redshift remains unclear. Here, we present results of circular dichroism (CD) and resonance Raman measurements on the purified LH1 complexes in a reaction center-associated form from a mesophilic and a thermophilic Blastochloris species. Both the LH1 complexes displayed purely positive CD signals for their Q_y transitions, in contrast to those of BChl a-containing LH1 complexes. This may reflect differences in the conjugation system of the bacteriochlorin between BChl b and BChl a and/or the differences in the pigment organization between the BChl b- and BChl a-containing LH1 complexes. Resonance Raman spectroscopy revealed remarkably large redshifts of the Raman bands for the BChl b C3-acetyl group, indicating unusually strong hydrogen bonds formed with LH1 polypeptides, results that were verified by a published structure. A linear correlation was found between the redshift of the Raman band for the BChl C3-acetyl group and the change in LH1-Q_y transition for all native BChl a- and BChl b-containing LH1 complexes examined. The strong hydrogen bonding and π–π interactions between BChl b and nearby aromatic residues in the LH1 polypeptides, along with the CD results, provide crucial insights into the spectral and structural origins for the ultra-redshift of the long-wavelength absorption maximum of BChl b-containing phototrophs.

含细菌叶绿素 (BChl) b的紫色光养细菌中的核心捕光复合物 (LH1) 的特征是在 1010 nm 附近具有最大近红外吸收。这种超红移的决定性原因尚不清楚。在这里，我们展示了对纯化的 LH1 复合物的圆二色性 (CD) 和共振拉曼测量结果，该复合物来自嗜温和嗜热的蓝藻物种的反应中心相关形式。与含有BChl a的 LH1 复合物相比，这两种 LH1 复合物的 Q _y跃迁都显示出纯正的 CD 信号。这可能反映了 BChl b和 BChl之间菌绿素结合系统的差异a和/或含BChl b和 BChl a的 LH1 复合物之间色素组织的差异。共振拉曼光谱揭示了 BChl b C3-乙酰基的拉曼谱带发生了非常大的红移，表明与 LH1 多肽形成了异常强的氢键，结果已由已发表的结构验证。在 BChl C3-乙酰基的拉曼谱带红移与所有被检测的含有BChl a和 BChl b的天然LH1 复合物的LH1-Q _y跃迁变化之间发现了线性相关性。BChl b之间的强氢键和 π-π 相互作用LH1 多肽中的芳香族残基和附近的芳香族残基，连同 CD 结果，提供了对含BChl b光养生物的长波长吸收最大值的超红移的光谱和结构起源的重要见解。