Recent advances in the characterization of the hexadecahemic cytochrome c from Desulfovibrio.

The biochemical characterization of the high molecular mass cytochromes c (Hmc) isolated from Desulfovibrio vulgaris has led to some controversy as regards their molecular size and subunit structure as well as their heme content and redox properties. Recently developed genetic techniques have made it possible to reach some definite conclusions about the structural and functional properties of the cytochrome. The hexadecahemic Hmc comprises four domains which resemble the tetrahemic cytochrome c3: the structure-function relationship between these multihemic proteins is examined. An hypothesis is discussed according to which the Hmc might be a peripherally interacting protein associated with the outer face of the cytoplasmic membrane, where it might interact with periplasmic proteins - [Fe] hydrogenase - and membrane-bound components of the hmc operon.