Plays a key role in regulating maximal capacity for electron transport and oxidative phosphorylation (By similarity). May be involved in Fe-S cluster shuttling and/or in redox reactions. Binds 1 [2Fe-2S] cluster per subunit. The [2Fe-2S] cluster is redox-active and pH labile and is significantly less stable at pH 4.5 as compared with pH 7.0. E is 0 +/- 10 mV for 2Fe-2S at pH 7.5. Homodimer. Expression is reduced in cells derived from cystic fibrosis patients. Expression is down-regulated by glibenclamide and 5-[(4-carboxyphenyl)methylene]-2-thioxo-3-(3-trifluoromethyl)phenyl-4-thiazolidinone (CFTR(inh)172), and up-regulated by cAMP/isoproterenol/IBMX, components that inhibit and stimulate chloride transport activity respectively. Ubiquitinated by PRKN during mitophagy, leading to its degradation and enhancement of mitophagy. Deubiquitinated by USP30. Binds pioglitazone, an anti-diabetes drug. Binding increases the stability of the 2Fe-2S cluster. Belongs to the CISD protein family.