We discovered natural photosynthesis using Zn-containing bacteriochlorophyll a in an acidophilic bacterium Addiphilium rubrum. Chemical analysis of the cell extracts gave a 13 : 2 :1 molar ratio of Zn-bacteriochlorophyll a : Mg-bacteriochlorophyll a : bacteriopheophytin a. Most of the pigments are associated with fully active reaction center and light-harvesting complexes analogous to those in purple photosynthetic bacteria. The finding indicates an unexpectedly wide variability of

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... s. Photosynthesis has been converting solar energy to chemical energy since its evolution on the early Earth, by use of the functions of Mg-containing porphyrin derivatives, namely, chlorophylls. The appropriate oxidation-reduction potentials and long-lived excited states of chlorophylls are favorable for the electron transfer reactions and the light-harvesting. These may be the reason for the photosynthetic organisms to choose chlorophylls among others. Among the chlorophyll derivatives containing metals other than Mg, only Zn-containing chlorophylls have chemical features comparable to Mg-chlorophylls (Watanabe and Kobayashi 1991). Zn-porphyrin derivatives are usually more stable than Mg-derivatives, and have been widely used in the studies of artificial photosynthesis (Wasielewski and Niemczyk 1984, Osuka et al. 1993). Zn-containing bac-Abbreviations: BChl, bacteriochlorophyll a; BPhe, bacteriopheophytin a.