Import of cytochrome c into mitochondria

The covalent attachment of heme to apocytochrome c, and therefore
the import of cytochrome c into mitochondria, is dependent on both
NADH plus a cytosolic cofactor that has been identified to be FMN
or FAD. NADH in concert with flavin nucleotides mediates the
reduction of heme. Heme in the reduced state is a prerequisite for
its covalent attachment to apocytochrome c by the enzyme cytochrome
c heme lyase and thus for subsequent translocation of cytochrome c
across the outer mitochondrial membrane during import.