NDUFB6 and ischemia: C-I contains 1 molecule of noncovalently bound FMN per molecule of the enzyme,36 and it is the main source of membrane-associated flavin in mitochondria.37 FMN release is likely to occur in ischemia because of complex I over-reduction via reverse electron transfer.38 Reductive dissociation of C-I FMN has been reported in vitro27,38 but has not been shown in physiological settings.