Apocytochrome c

The cytochrome c import pathway differs markedly from the general
route taken by the majority of other imported proteins, which is
characterized by the import involvement of namely, surface
receptors, the general insertion protein (GIP), contact sites and
by the requirement of a membrane potential (Δψ). Unique features of
both the cytochrome c precursor (apocytochrome c) and of the
mechanism that transports it into mitochondria, have contributed to
the evolution of a distinct import pathway that is not shared by
any other mitochondrial protein analysed thus far. The cytochrome c
pathway is particularly unique because i) apocytochrome c appears
to have spontaneous membrane insertion-activity; ii) cytochrome c
heme lyase seems to act as a specific binding site in lieu of a
surface receptor and; iii) covalent heme addition and the
associated refolding of the polypeptide appears to provide the free
energy for the translocation of the cytochrome c polypeptide across
the outer mitochondrial membrane.