Fig. 6.

Respiration-triggered heme transfer in yeast mitochondria. H₂O₂ generated during mitochondrial respiration oxidizes Ccp1 to compound I (CpdI). The oxidizing equivalents from H₂O₂ can be reduced by Cyc1^II or transferred to the peroxidase’s residues, including the proximal Fe ligand His175 to yield oxo-histidine. Formation of the latter labilizes the heme group, which is transferred either directly or via unidentified intermediate(s) to apoCta1 (path A), and the nascent Cta1 activity detoxifies H₂O₂. ApoCcp1 has low conformational stability and undergoes reverse translocation to the vacuole (path B) and the nucleus (path C).