Purification and properties of a low-redox-potential tetraheme cytochrome c3 from Shewanella putrefaciens

Shewanella putrefaciens is a facultatively anaerobic bacterium in the gamma group of the proteobacteria, capable of utilizing a wide variety of anaerobic electron acceptors. An examination of its cytochrome content revealed the presence of a tetraheme, low-redox-potential (E'o = -233 mV), cytochrome c-type cytochrome with a molecular mass of 12,120 Da and a pI of 5.8. The electron spin resonance data indicate a bis-histidine coordination of heme groups. Reduction of ferric citrate was accompanied by oxidation of the cytochrome. The biochemical properties suggested that this protein was in the cytochrome c3 group, which is supported by N-terminal sequence data up to the first heme binding site.