Redox-active quinones play essential roles in efficient light energy conversion in type-II reaction centers of purple phototrophic bacteria. In the light-harvesting 1 reaction center (LH1-RC) complex of purple bacteria, Q_B is converted to Q_BH₂ upon light-induced reduction and Q_BH₂ is transported to the quinone pool in the membrane through the LH1 ring. In the purple bacterium Rhodobacter sphaeroides, the C-shaped LH1 ring contains a gap for quinone transport. In contrast, the thermophilic purple bacterium Thermochromatium (Tch.) tepidum has a closed O-shaped LH1 ring that lacks a gap, and hence the mechanism of photosynthetic quinone transport is unclear. Here we detected light-induced Fourier transform infrared (FTIR) signals responsible for changes of Q_B and its binding site that accompany photosynthetic quinone reduction in Tch. tepidum and characterized Q_B and Q_BH₂ marker bands based on their ¹⁵N- and ¹³C-isotopic shifts. Quinone exchanges were monitored using reconstituted photosynthetic membranes comprised of solubilized photosynthetic proteins, membrane lipids, and exogenous ubiquinone (UQ) molecules. In combination with ¹³C-labeling of the LH1-RC and replacement of native UQ₈ by ubiquinones of different tail lengths, we demonstrated that quinone exchanges occur efficiently within the hydrophobic environment of the lipid membrane and depend on the side chain length of UQ. These results strongly indicate that unlike the process in Rba. sphaeroides, quinone transport in Tch. tepidum occurs through the size-restricted hydrophobic channels in the closed LH1 ring and are consistent with structural studies that have revealed narrow hydrophobic channels in the Tch. tepidum LH1 transmembrane region.

氧化还原活性醌在紫色光养细菌的II型反应中心中，在有效的光能转换中起着至关重要的作用。在紫色细菌的集光1反应中心（LH1-RC）络合物中，光诱导还原后Q _B转化为Q _B H ₂，并且Q _B H ₂通过LH1环转移到膜中的醌库中。在紫色细菌球形红细菌（Rhodobacter sphaeroides）中，C形LH1环包含一个间隙，用于醌运输。与此相反，嗜热紫细菌Thermochromatium（Tch的。）绿硫菌来源具有没有间隙的闭合的O形LH1环，因此光合醌运输的机理尚不清楚。在这里，我们检测到光诱导的傅立叶变换红外（FTIR）信号，该信号负责Q _B及其结合位点的变化，并伴随着Tch中光合醌的还原。绿硫菌来源和其特征在于Q_乙和Q_乙ħ ₂基于它们的标记带¹⁵ N-和¹³ C-同位素位移。使用由溶解的光合作用蛋白，膜脂质和外源性泛醌（UQ）分子组成的重组光合作用膜监测醌交换。与¹³结合LH1-RC的C-标记和不同尾长的泛醌替代天然UQ ₈，我们证明了醌交换在脂质膜的疏水环境内有效发生，并且取决于UQ的侧链长度。这些结果强烈表明，与Rba中的过程不同。sphaeroides，醌在Tch中运输。锡青霉菌通过封闭的LH1环中受尺寸限制的疏水通道发生，并且与揭示Tch中疏水通道狭窄的结构研究一致。温热的LH1跨膜区。