Mitochondrial cytochrome c synthase: CP motifs are not necessary for heme attachment to apocytochrome c

► CP motifs, including in holocytochrome c synthase, can have roles in heme binding. ► CP motifs of holocytochrome c synthase are not required for heme attachment activity. ► CP motifs in HCCS may have a separate role in heme binding in mitochondria. ► Mutations associated with the human disease MLS abolish the activity of HCCS.