Ferredoxin from Methanosarcina barkeri: evidence for the presence of a three-iron center.

TLDR: The combined EPR and Mössbauer studies show that M. barkeri ferredoxin contains only [3Fe-3S] clusters, similar to Azotobacter vinelandii Fd and mitochondrial beef heart aconitase.

Abstract: Methanosarcina barkeri ferredoxin was purified and characterized by electron paramagnetic resonance (EPR) and Mossbauer spectroscopy. The purification procedure included chromatographic steps on DEAE-cellulose and gel filtration. The isolated protein is unstable under aerobic conditions. The ferredoxin exhibits charge transfer bands at 283 nm and 405 nm with an absorption ratio A405/A283= 0.73. Its molecular weight has been estimated to be 20000–22000 by gel filtration chromatography. The native ferredoxin exhibits an intense EPR signal at g= 2.02 and only a very weak g= 1.94 signal develops upon reduction with dithionite. The Mossbauer spectra of the reduced protein are characteristic of a [3 Fe-3S] center. The combined EPR and Mossbauer studies show that M. barkeri ferredoxin contains only [3 Fe-3S] clusters, similar to Azotobacter vinelandii Fd [Emptage, M. H., Kent, T. A., Huynh, B. H., Rawlings, J., Orme-Johnson, W. H. & Munck, M. (1980) J. Biol. Chem. 255, 1793–1796], Desulfovibrio gigas FdII [Huynh, B. H., Moura, J. J. G., Moura, I., Kent, T. A., LeGall, J., Xavier, A. V. & Munck, E. (1980) J. Biol. Chem. 255, 3242–3244] and mitochondrial beef heart aconitase [Kent, T. A., Dreyer, J.-L., Kennedy, M. C., Huynh, B. H., Emptage, M. H., Beinert, H. & Munck, E. (1982) Proc. Natl Acad. Sci. USA, 79, 1096–1100].