The Amino Acid Sequence of Chromatium Ferredoxin

Abstract

The amino acid sequence of Chromatium ferredoxin was determined by studies of thermolysin peptides of S-carboxymethylcysteinylferredoxin and chymotryptic peptides of oxidized ferredoxin. The 81 amino acid residues in the molecule have the following sequence: Ala-Leu-Met-Ile-Thr-Asp-Gln-Cys-Ile-Asn-Cys-Asn-Val-Cys-Gln-Pro-Glu-Cys-Pro-Asn-Gly-Ala-Ile-Ser-Gln-Gly-Asp-Glu-Thr-Tyr-Val-Ile-Glu-Pro-Ser-Leu-Cys-Thr-Glu-Cys-Val-Gly-His-Tyr-Glu-Thr-Ser-Gln-Cys-Val-Asp-Cys-Val-Glu-Val-Cys-Pro-Ile-Lys-Asp-Pro-Ser-His-Glu-Glu-Thr-Glu-Asp-Glu-Leu-Arg-Ala-Lys-Tyr-Glu-Arg-Ile-Thr-Gly-Glu-Gly. The molecular weight, excluding iron and inorganic sulfide, was calculated to be 8943. The 9 cysteinyl residues are located in a somewhat different manner from those of the ferredoxins of nonphotosynthetic bacteria. However, this sequence is apparently homologous to those of nonphotosynthetic bacterial ferredoxins. Some structural features of bacterial ferredoxins are compared.