Heme biosynthesis pathway. ALA: 5-aminolevulinic acid, ALAS: ALA synthase, PBGS: porphobilinogen synthase, ALAD: ALA dehydratase, PBGD: porphobilinogen deaminase, UROS: uroporphyrinogen synthase, UROD: uroporphyrinogen decarboxylase, PBR: peripheral-type benzodiazepine receptor, CPO: coproporphyrinogen III oxidase, PPO: protoporphyrinogen IX oxidase, FC: Ferrochelatase, IMM: inner mitochondrial membrane, IMS: intermembrane space, OMM: outer mitochondrial membrane.