Ferredoxins from the photosynthetic purple non-sulfur bacterium Rhodopseudomonas palustris. Isolation and amino acid sequence of ferredoxin I.

Two ferredoxins, ferredoxins I and II, were prepared from Rhodopseudomonas palustris. They were separated on a Sephadex column after carboxymethylation and ferredoxin I, the major component, was subjected to an amino acid sequence study. The protein was composed of 63 amino acid residues and the sequence was as follows: (sequence; see text). The molecular weight was calculated to be 6,718, excluding iron and sulfur atoms. The distribution of the nine cysteine residues was similar to but clearly distinct from those of ferredoxins of other photosynthetic bacteria. Comparison of this ferredoxin with those of other bacteria suggests that the photosynthetic bacteria evolved on separate lines. Ferredoxin II was also subjected to analyses of amino acid composition and terminal sequences, but no further study was possible due to the limited material. Although the composition was different from that of ferredoxin I, the terminal sequences were exactly the same as those of ferredoxin I.