Reconstitution of synthesized quinones to photosynthetic reaction center I

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We have developed a method to extract and reconstitute phylloquinone which tightly binds to the plant photosynthetic photosystem I reaction center complex. The quinone, which has been known to function as vitamin K1 when fed by animal, is shown to function as the secondary electron acceptor in the photosystem I photochemistry in plant. This has made clear that all the reaction center complexes of photosynthetic organisms, from photosynthetic purple and green bacteria to higher green plants, use quinone as the secondary electron acceptor. This gives a new basis for the study of evolution of photosynthetic system as discussed in this study.After extracting phylloquinone from photosystem I reaction center, we introduced various quinone and analog compounds. They almost fully substituted for phylloquinone. Relation between the physicochemical properties and structure of these compounds and their electron transfer ability at the phylloquinone binding site in the reaction center was studied. It isoindicated that the photosynthetic reaction center proteins give unique new reaction environments for the introduced compounds. This system can also be used to test the reaction of artificial compounds in proteinaceous environments and enables the reactions impossible in solution.Structure and function of iron-sulfur clusters which function as the tertiary electron acceptors in photosystem I reaction center were also studied by cryogenic EPR.