Blastochloris tepida is a newly described thermophilic purple bacterium containing bacteriochlorophyll b. Using purified light-harvesting 1 reaction center (LH1-RC) core complexes from Blc. tepida, we compared the biochemical, spectroscopic, and thermal denaturation properties of these complexes with those of its mesophilic counterpart, Blc. viridis. Besides their growth temperature optima, a striking difference between the two species was seen in the carotenoid composition of their LH1-RC complexes. The more thermostable Blc. tepida complex contained more carotenoids with longer conjugation lengths (n > 9), such as lycopenes (n = 11), and had a total carotenoid content significantly higher than that of the Blc. viridis complex, irrespective of the light intensity used for growth. The thermostability of LH1-RCs from both Blc. tepida and Blc. viridis decreased significantly in cells grown in the presence of diphenylamine, a compound that inhibits the formation of highly conjugated carotenoids. In contrast to the thermophilic purple bacterium Thermochromatium tepidum, where Ca²⁺ is essential for LH1-RC thermostability, Ca²⁺ neither was present in nor had any effect on the thermostability of the Blc. tepida LH1-RC. These results point to a mechanism that carotenoids with elongated conjugations enhance hydrophobic interactions with proteins in the Blc. tepida LH1-RC, thereby allowing the complexes to withstand thermal denaturation. This conclusion is bolstered by a structural model of the Blc. tepida LH1-RC and is the first example of photocomplex thermostability being linked to a carotenoid-based mechanism.

中文翻译：

---

番茄红素家族类胡萝卜素赋予新型嗜热紫色细菌光配合物热稳定性。

棉叶杆菌球茎杆菌是一种新近描述的含有细菌叶绿素b的嗜热紫色细菌。使用来自Blc的纯化的光捕获1反应中心（LH1-RC）核心配合物。tepida，我们比较了生化，光谱，和这些复合物与它对应温的热变性性质BLC。绿藻。除了它们的生长温度最适外，在它们的LH1-RC配合物的类胡萝卜素组成中发现了这两个物种之间的显着差异。Blc越热稳定。tepida复合物包含更多的具有更长共轭长度（n > 9）的类胡萝卜素，例如番茄红素（n= 11），并且总类胡萝卜素含量明显高于Blc。翠绿复合体，与用于生长的光强度无关。两个Blc的LH1-RCs的热稳定性。tepida和Blc 。在二苯胺（一种抑制高度共轭类胡萝卜素的形成的化合物）存在下生长的细胞中，绿色病毒明显减少。与嗜热性紫色细菌嗜热铬细菌（Thermorchromatium tepidum）相比，Ca ²⁺对于LH1-RC热稳定性是必不可少的，而Ca ²⁺既不存在也不对Blc的热稳定性有任何影响。特皮达LH1-RC。这些结果表明具有延长的缀合的类胡萝卜素增强与Blc中的蛋白质的疏水相互作用的机制。tepida LH1-RC，从而使配合物经受热变性。Blc的结构模型支持了这一结论。tepida LH1-RC，是光配合物热稳定性与基于类胡萝卜素的机制相关的第一个例子。