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

通过引入进化的概念，可以很好地理解光合作用中的反应机制，从光合作用细菌到产氧光合作用生物的反应中心复合体的连续性表明了这一点。在氧合光合作用的反应机制方面还存在许多空白，如：氧合光合作用的起源、水氧化机制的起源、次生内生共生对Ch1a/c藻类的进化等。为了接近这些巨大的差距，比较几组产氧微生物的反应性质是一个好主意。我们试图通过实验方法和小组讨论来了解几个关键点的反应机理。(1)研究了细胞色素C550在环藻和红藻中的定位及其在反应中心II的化学计量学。在红藻紫球藻中，由于…的存在，其定位不一定清楚更多的是它的低含量。另一方面，在蓝藻中，聚球藻。PCC6803，与这种细胞色素相关的基因有很多，但单个组分的功能不一定清楚。(2)1999年夏天，在阿拉斯加大学费尔班克斯举行的一次小型研讨会上进行了一次小组讨论。根据本研究成员所获得的结果，我们通常理解以下几点。(I)在光合细菌的进化过程中，根据色素生物合成途径的基因结构，被认为是细菌最古老的祖先的橙色绿藻可能不是这样的。(Ii)产氧光合原核生物可能在进化的早期获得了几个色素合成基因。(3)甲藻的基因结构是独特的，一个基因由一个环组成。这是完全意想不到的性质，但其生物学意义尚不清楚。基于上述结果和讨论，所有成员同意在下一次机会继续进行这种合作研究。较少

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