Molecular biology of c-type cytochromes from Desulfovibrio vulgaris Hildenborough.

Sulfate reducing bacteria of the genus Desulfovibrio harbor a wide variety of redox proteins. Three different c-type cytochromes, cytochrome c-553, cytochrome c3 and the high molecular mass cytochrome have been isolated from these bacteria. The high molecular mass cytochrome is part of an operon that encodes a transmembrane protein complex that mediates electron transfer across the cytoplasmic membrane. The physiological function of the other two cytochromes is less clear. They are encoded by monocistronic genes and their redox partners can thus not be identified by gene sequencing. Expression of genes for c-type cytochromes in a foreign host are complicated due to the requirement for covalent heme insertion. Cytochrome c-553 is readily expressed in Escherichia coli in functional form, but cytochrome c3 and the high molecular mass cytochrome are for reasons that are presently not clear.