Optimization mechanism of electron transfer proteins

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Optimization mechanisms of intra-protein electron transfer were studied in four systems below. (1) plant photosystems I and II reaction centers. (2) reaction center complexes of green sulfur bacteria. (3) A new type of photosynthetic purple bacteria that uses Zn-containing bacteriochlorophylls. (4) a new type of cyanobacteria that uses chlorophyll d which absorbs far-red light, In all the photosynthetic organisms thus far known, chlorophylls are known to be essential. We, however, showed (1) proteins function to optimize the reaction environment of chlorophylls through quinone-exchange studies in the plant photosystem I and H reaction centers, (2) Zn- bacteriochlorophyll can replace the function of Mg-bacteriochlorophyll in vivo, and (3) chlorophyll d also supports the oxygenic photosynthesis as efficient as that by chlorophyll a. These results indicate that natural photosynthetic systems have more varieties than ever estimated and that the photosynthesis with new types of chlorophylls were enabled by a minor tuning of the protein structure around chlorophylls or quinones inside the reaction center protein.