Plays a key role in regulating maximal capacity for electron transport and oxidative phosphorylation. May be involved in Fe-S cluster shuttling and/or in redox reactions (By similarity). Binds 1 [2Fe-2S] cluster per subunit. Homodimer. Ubiquitinated by PRKN during mitophagy, leading to its degradation and enhancement of mitophagy. Deubiquitinated by USP30. Binds pioglitazone, an anti-diabetes drug. Belongs to the CISD protein family.