THE PRIMARY STRUCTURE OF THE SPLIT-SORET CYTOCHROME-C FROM DESULFOVIBRIO-DESULFURICANS ATCC-27774 REVEALS AN UNUSUAL TYPE OF DIHEME CYTOCHROME-C

The complete amino acid sequence of the unusual diheme split-Soret cyt ochrome c from the sulphate-reducing Desulfovibrio desulfuricans strai n ATCC 27774 has been determined using classical chemical sequencing t echniques and mass spectrometry. The 247-residue sequence shows almost no similarity with any other known diheme cytochrome c, but the heme- binding site of the protein is similar to that of the cytochromes c, f rom the sulphate reducers. The cytochrome-c-like domain of the protein covers only the C-terminal part of the molecule, and there is evidenc e for at least one more domain containing four cysteine residues, whic h might bind another cofactor, possibly a non-heme iron-containing clu ster. This domain is similar to a sequence fragment of the genome of A rchaeoglobus fulgidus, which confirms the high conservation of the gen es involved in sulfate reduction.