Electron transport components from methanogenic bacteria: The ferredoxin from [formula omitted] (strain Fusaro)

Abstract

A ferredoxin has been isolated from the methanogenic organism Methanosarcina barkeri (strain Fusaro). The protein appears to be constituted by two identical subunits of molecular weight approx. 6000 daltons. The UV-visible spectrum of the protein is characterized by two broad absorption peaks centered at 410 and 300 nm and an absorbance ratio A 410 A 300 = 0.8 . The molar extinction coefficients at 410 and 300 nm are 36,500 and 45,625 M −1 cm −1, respectively. The amino acid compsition of M. barkeri ferredoxin shows a preponderance of acidic residues and lacks five amino acids. The protein contains 8 cysteine residues and approx. 7 iron atoms and 7–8 acid-labile sulfide groups per molecule which are indicative of the presence of two iron-sulfur clusters in the molecule. The N-terminal sequence shows a high degree of homology with the sequences of ferredoxins from Clostridium pasteurianum, Desulfovibrio gigas and Desulfovibrio africanus. M. barkeri ferredoxin functions as an electron carrier in the pyruvate dehydrogenase system. Its possible role in a variety of electron transfer reactions is discussed.