Purification, Amino-Acid Sequence and Some Properties of the Ferredoxin Isolated fromBacillus acidocaldarius

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Abstract
Ferredoxin was isolated from the aerobic, thermophilic and acidophilic bacterium B. acidocaldarius and its sequence of 78 amino acids completely determined by automated Edman degradation of the protein and of peptides derived from chemical cleavage between aspartic acid and proline and from enzymatic digestions. The optical spectrum of the oxidized protein has a broad maximum around 400 nm. The ferredoxin is thermostable: its absorbance begins to decrease only at incubation > 71.degree. C. The number of Fe and inorganic S atoms/molecule was determined to be 5.3 and 5.0, respectively. The calculated molar extinction coefficient was 23,000 M-1 .times. cm-1, the MW of the apoferredoxin 8872 daltons. Contrary to all expectations, the sequence of B. acidocaldarius ferredoxin shows very little homology to that of B. stearothermophilus but closely resembles that of Thermus thermophilus.