Adaptation of photosynthesis to oxidative environment

光合作用在厌氧环境下进化，然后适应氧化环境。在本研究中，我们试图阐明环境中氧分子对绝对厌氧绿硫菌（Chlorobium）、兼性厌氧绿丝状菌（Chloroflexus）以及兼性厌氧紫色菌（purple bacteria）的激发态能量传递和光合电子传递的影响。这项研究是日本、丹麦、法国和意大利科学家的国际合作项目。以下是我们得到的主要结果。(1)在绿硫细菌的光收集工具——绿体中，光合色素的荧光会根据环境中氧分子的存在与否而发生十倍以上的变化。为了弄清这种荧光变化是否真的影响光合电子转移的效率，我们通过改变环境中的氧化还原电位来测量光合电子转移对光强的依赖性。结果表明，氧通过影响激发能转移来调节电子转移效率。(2)在绿色丝状菌中，不存在这种调节。然而，当人工醌加入到叶绿体或整个细胞中时，观察到类似的调节，表明醌负责调节。(3)这些醌类化合物可能与细菌叶绿素c分子相互作用。(4)为阐明紫色光合细菌对环境中氧化还原条件变化的适应性，对不同种类的光合反应中心结合的细胞色素亚基进行了表征。我们发现，在适应氧化还原环境的Rhodovulum sulfidophilum中，亚基上只有3个血红素，而不是其他许多物种的4个血红素。提示氧化环境可能导致亚基进化过程中血红素的减少。少

Photosynthesis has been evalved under anaerobic environment, and thereafter adapted to oxidative environment. In this study, we have tried to clarify the effect of oxigen molecules in the environment on the excited energy transfer and the photosynthetic electron transfer in the absolute anaerobic green sulfur bacteria, Chlorobium, and the facultatively anaerobic green filamentous bacteria, Chloroflexus, as well as the facultatively anaerobic purple bacteria. Research was done as an international collaborative project among scientists of Japan, Denmark, France and Italy. Followings are main results we obtained.(1)In the light-harvesting appratus of green sulfur bacteria, called chlorosomes, it was known the fluorescence from the photosynthetic pigments is changed by a factor of more than ten depending on the presence or absence of oxygen molecules in the environment. To clarify if this fluoresence changes really affect the efficiency of the photosynthetic electron transfer, we measured … More the light intensity dependence of the photosynthetic electron transfer by changing the redox potential in the environment. It was shown that oxygen regulates the efficiency of electron transfer by affecting the excitation energy transfer.(2)In the green filamentous bacteria, such a regulation was not present. However, when artificial quinone was added to the chlororsomes or whole cells, a similar regulation was observed, indicating that quinone is responsible for the regulation.(3)Such quinones were suggested to be interacted with bacteriochlorophyll c molecules.(4)To clarify the adaptation of purple photosynthetic bacteria to the changes of redox conditions in the environment, cytochrome subunit bound to the photosynthetic reactio center was characterized in various species. We found in a species, Rhodovulum sulfidophilum, which well adapted to oxidative and reductive environment, only three hemes are bound to the subunit instead of the four hemes in the other many species. It was suggested the oxidative environment may have reduced the heme in the subunit evolutionary. Less