Mechanism of zinc-insertion into porphyrin ring in acidophilic photosynthetic bacteria

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The aim :Final aim of this research is to elucidate the mechanism of biosynthesis of zinc-bacteriochlorophyll in acidophilic photosynthetic bacteria.Results and scope :1. In Acidiphilium rubrum, there was a single copy of magnesium chelatase subunit genes and these were functional in this bacterium.2. Only magnesium-protoporphyrin IX and its monomethyl ester accumulated but not zinc-protoporphyrin IX or its monomethylester in the bacterium. Protoporphyrin IX monomethyl ester was also detected as an intermediate. These suggested magnesium was exchanged by zinc after magnesium insertion to form zinc-bacteriochlorophyll.3. Whether the exchange takes place in enzymatically or non-enzymatically could not be determined, but it was possible that in the low pH environment, where zinc-bacteriochlorophyll might be formed, the exchange take places very easily and non-enzymatically.4. We tried to detect intermediates containing zinc-tetrapyrroles in this bacterium to identify the exchange reaction but so far we could not.