The reaction mechanisms of the oxygenic photosynthesis. - Analyses based on the phylogeny of chloroplast proteins

通过引入进化的思想，我们可以很好地理解光合作用的反应机制，从光合细菌到氧光合生物的反应中心络合物的连续性就表明了这一点。在含氧光合作用的反应机制方面，如含氧光合生物的起源、水氧化机制的起源、Ch1 a/c藻类通过次生内共生的进化等，还存在许多较大的空白。为了接近这些巨大的差距，比较几组含氧生物之间的反应特性是一个好主意。我们试图通过实验方法和小组讨论来了解几个临界点的反应机理。(1)研究了蓝藻和红藻中细胞色素c550的定位及其在反应中心ⅱ上的化学计量。在红藻卟啉（Porphyridium cruentum）中，由于其含量较低，定位并不明确。另一方面，在聚胞蓝杆菌PCC6803中，与该细胞色素相关的基因有多个，但单个组分的功能并不一定清楚。1999年夏天，在阿拉斯加费尔班克斯大学举行了一次小型研讨会，实现了小组讨论。根据本次研究成员所获得的结果，我们大致理解了以下几点。(1)在光合细菌的进化过程中，从色素生物合成途径的基因结构来看，被认为是细菌最古老祖先的金绿藻（Chloroflexus aurantiacus）可能并非如此。（ii）产氧光合作用的原核生物在进化早期可能获得了几个色素合成基因。（iii）鞭毛藻的基因结构是独特的；一个基因由一个环组成。这是完全出乎意料的性质，但其生物学意义尚不清楚。基于以上的结果和讨论，所有成员都同意在下次有机会时继续进行这种合作研究。少

Reaction mechanisms in photosynthesis will be well understood by introducing the idea of evolution, as shown by the continuity of reaction center complexes from photosynthetic bacteria to oxygenic photosynthetic organisms. There remain many large gaps in the reaction mechanisms in oxygenic photosynthesis, for example, an origin of oxygenic photosynthetic organisms, an origin of water oxidation machinery, evolution of Ch1 a/c algae by the secondary endosymbiosis, and so on. To approach to these large gaps, it is a good idea to compare reaction properties among several groups of oxygenic organisms. We attempted to understand the reaction mechanisms of several critical points by experimental approach and by group discussion.(1) Localization of cytochrome c550, an essential protein for oxygen evolution in cyancibacteria and red algae, and its stoichiometry per reaction center II was investigated. In the red alga Porphyridium cruentum, its localization was not necessarily clear, because of … More its low content. On the other hand, in cyanobacteium Synechocystis sp. PCC6803, there are plural genes related to this cytochrome, however function of individual components were not necessarily clear.(2) A group discussion was realized by a mini-symposium held in the University of Alaska, Fairbanks, in the summer of 1999. Based on the results obtained by the members of this research, we commonly understood the following points. (I) In the course of evolution of photosynthetic bacteria, Chloroflexus aurantiacus, which was postulated to be the oldest ancestor of bacteria, might not be the case based on the gene structure of pigment biosynthetic pathways. (ii) Oxygenic photosynthetic prokaryote probably acquired several genes for pigment synthesis in the early stage of evolution. (iii) A gene structure of dinoflagellates was unique ; one-gene is composed of one-circle. This is completely unexpected property, but its biological significance was not yet clear.Based on the above results and discussion, all the members agreed to continue this kind of co-operative research for the next chance. Less