Cytochrome cy of Rhodobacter capsulatus is attached to a cytoplasmic membrane by an uncleaved signal sequence-like anchor

The biologically active, C-terminally epitope-tagged derivative (FLAGed cyt cy) of Rhodobacter capsulatus cytochrome (cyt) cy was purified and analyzed to characterize the binding properties of the cyt to the cytoplasmic membrane. The purified Rhodobacter capsulatus FLAGed cyt cy exhibited optical spectral properties and redox midpoint potentials that were similar to c-type cytochromes from bacterial and plant mitochondrial sources. Furthermore, the purified mature cyt cy contained an N-terminal signal sequence-like extension that can anchor to the periplasmic membrane.