Functional properties of type I and type II cytochromes c3 from Desulfovibrio africanus

Type I cytochrome c3 is a key protein in the bioenergetic metabolism of Desulfovibrio spp., mediating electron transfer between periplasmic hydrogenase and multihaem cytochromes associated with membrane bound complexes, such as type II cytochrome c3. This work presents the NMR assignment of the haem substituents in type I cytochrome c3 isolated from Desulfovibrio africanus and the thermodynamic and kinetic characterisation of type I and type II cytochromes c3 belonging to the same organism. It is shown that the redox properties of the two proteins allow electrons to be transferred between them in the physiologically relevant direction with the release of energised protons close to the membrane where they can be used by the ATP synthase.