In total, eight iron-sulfur (4Fe-4S) clusters are incorporated into six subunits (mitochondrial matrix-located NDUFS1, S2, S7, S8 and mitochondrial membrane-located V1 and V2) (Andrews et al. 2013). Incorporation into NDUFS1, S2, S7 and S8 is shown in a separate reaction. The mechanism of transfer is unknown. NDUFV1 also binds FMN (Schuelke et al. 1998).