The ubiquinol-cytochrome C reductase complex (cytochrome bc1 complex) is an essential component of the mitochondrial cellular respiratory chain. This family represents the 6.4kD protein, which may be closely linked to the iron-sulphur protein in the complex and function as an iron-sulphur protein binding factor [1].

1: Crystallographic studies of quinol oxidation site inhibitors: a modified classification of inhibitors for the cytochrome bc(1) complex. Esser L, Quinn B, Li YF, Zhang M, Elberry M, Yu L, Yu CA, Xia D; J Mol Biol. 2004;341:281-302. PMID:15312779