FERREDOXIN FROM PHOTOSYNTHETIC BACTERIUM, CHLOROBIUM THIOSULFATOPHILUM - A LINK TO FERREDOXINS FROM NONPHOTOSYNTHETIC BACTERIA

1. Ferredoxin from the green photosynthetic bacterium, Chlorobium thiosulfatophilum, was purified and certain of its properties were determined. The purest preparations showed a ratio of A385 mμ/A280 mμ of 0.71 and contained 4.5 iron and acidlabile sulfide groups per molecule. 2. Like ferredoxins from nonphotosynthetic anaerobic bacteria, Chlorobium ferredoxin showed a molecular weight of 6000 (based on amino acid composition and amino-terminal alanine) and lacked the full complement of amino acids. Chlorobium ferredoxin contained 13 different amino acids and was devoid of lysine, histidine, arginine, tryptophan and methionine. As for all ferredoxins examined, the aminoterminal end group of Chlorobium ferredoxin was alanine. 3. Chlorobium ferredoxin resembled Chromatium ferredoxin in its absorption spectrum (peaks at 385 and 280 mμ, shoulder at 300 mμ), in having glycine as C-terminal end group, and in its redox properties. Chlorobium ferredoxin was reduced photochemically with chloroplast suspensions but not with sodium dithionite. 4. The characteristics of Chlorobium ferredoxin are consistent with the view that it is a link between the ferredoxins of nonphotosynthetic anaerobic bacteria and those of photosynthetic bacteria of the Chromatium-type. The possible evolutionary significance of these findings is discussed. © 1969.