PARENT SESSION
Posters P2A Type I reaction centres. Abstracts (181-218)

Purification of two ferredoxins and cloning their genes from the photosynthetic bacterium Heliobacillus mobilis. Atsushi Hatano¹, Daisuke Seo², Masaharu Kitashima^*,1, Hidehiro Sakurai², Kazuhito Inoue¹, ¹ Dept. Biol. Sci., Hiratsuka, Kanagawa, Japan² Dept. Biol., Shinjuku, Tokyo, Japan

ABSTRACT- Heliobacteria belong to a relatively recently found new group of phototrophic bacteria, in which they occupy a unique position in that they belong to Gram-positive ones. The reaction center (RC) of heliobacteria belongs to Type-1 RC as do those of green sulfur bacteria and of photosystem I of oxygen-evolving photosynthetic organisms. As the RC of heliobacteria contains iron-sulfur cluster(s), it is assumed that they directly reduce Fd as do other Type-1 RCs, but it has not yet been proven biochemically. As heliobacteria constitute a unique lineage in phototrophic prokaryotes, we have isolated two Fds (Fd1 and Fd2) from Heliobacillus mobilis and determined their N-terminal amino acid sequences as well as their genomic DNA sequences. They belong to the 2[4Fe-4S] type with absorption maxima at about 280 and 385 nm. Both of them support NADP⁺ photoreduction in a heterologous assay system containing reaction center particles and Fd-NADP⁺ reductase. Fd1 was relatively resistant to oxygen and its A₃₈₅ value did not significantly decrease under air, while Fd2 was sensitive to oxygen with its A₃₈₅ value reduced under the same conditions. We have also sequenced the genes encoding these Fds using a primer-walking strategy. The Fd1 and Fd2 genes are arranged in tandem. The phylogenetic relationship between the Fd1 and Fd2 genes and the relationship of these two genes with other Fds are discussed.

KEY WORDS: heliobacteria, ferredoxin, electron transport, photosynthetic bacteria