Amino Acid Sequence of the Major Component of Aphanothece sacrum Ferredoxin1

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Abstract
The amino acid sequence of the major ferredoxin component isolated from a blue-green alga, Aphanothece sacrum, has been fully determined. Chymotryptic and tryptic peptides of carboxymethyl-ferredoxin and chymotryptic peptides of oxidized ferredoxin were prepared and their sequences were analyzed. Together with previous work on the amino terminal sequence, established with a sequence analyzer, these peptide sequences permitted the complete amino acid sequence of this ferredoxin to be deduced. It was composed of 96 amino acid residues with five cysteine residues. The cysteine residue at the 18th position usually found in other chloroplast-type ferredoxins was replaced by a valine residue and the cysteine residue at the 85th position was common with that in Scenedesmus ferredoxin. The sequence was Ala-Ser-Tyr-Lys-Val-Thr-Leu-Lys-Thr-Pro-Asp-Gly-Asp-Asn-Val-Ile-Thr-Val-Pro-Asp-Asp-Glu-Tyr-Ile-Leu-Asp-Val-Ala-Glu-Glu-Glu-Gly-Leu-Asp-Leu-Pro-Tyr-Ser-Cys-Arg-Ala-Gly-Ala-Cys-Ser-Thr-Cys-Ala-Gly-Lys-Leu-Val-Ser-Gly-Pro-Ala-Pro-Asp-Glu-Asp-Gln-Ser-Phe- Leu- Asp- Asp-Asp-Gin- Ile-Gln- Ala-Gly-Tyr-Ile-Leu-Thr-Cys-Val -Ala-Tyr -Pro-Thr-Gly-Asp-Cys-Val-Ile-Glu-Thr-His-Lys-Glu-Glu-Ala-Leu-Tyr. Calculation of the numbers of amino acid differences among chloroplast-type ferredoxins indicates that the Aphanothece ferredoxin is far divergent not only from higher plant ferredoxins but also from Spirulina ferredoxins, blue-green algal ferredoxins. Some comments on the evolution of ferredoxins are presented.