Escherichia coli Ferredoxin, an Iron‐Sulfur Protein of the Adrenodoxin Type

Ferredoxin of Escherichia coli is an iron‐sulfur protein of the molecular weight about 12000 which contains two iron and two labile sulfur atoms. The sequence of the amino terminus is HN‐Pro‐Lys‐Val‐Ile‐Val‐Leu‐Tyr‐. The electron paramagnetic resonance spectrum of the reduced form shows a low‐field signal with g∥= 2.02 and a single high‐field signal with g⊥= 1.94. From the circular dichroism spectrum in the peptide absorption region an amount of 10% helically ordered regions is computed. A new peak in the light absorption spectrum at 545 nm appears upon reduction. From the spectral data, which reflect the fine structure of the chromophore and the gross conformation of the polypeptide chain, a close relationship to the mitochondrial adrenodoxin is concluded. The midpoint potential of the protein is –0.38 V. It does not mediate electron transport in the NADP‐photoreduction system of spinach and is incapable of replacing the Pseudomonas putida ferredoxin in the camphor hydroxylation. The physiological role of this ferredoxin, which is not a functional analogue of the Escherichia coli flavodoxin and which is synthesized by aerobically as well as anaerobically growing cells, is unknown.