The ubiquinol-cytochrome C reductase complex (cytochrome bc1 complex) is a respiratory multienzyme complex [1]. This Pfam family represents the 'hinge' protein of the complex which is thought to mediate formation of the cytochrome c1 and cytochrome c complex.

1: Complete structure of the 11-subunit bovine mitochondrial cytochrome bc1 complex [see comments] Iwata S, Lee JW, Okada K, Lee JK, Iwata M, Rasmussen B, Link TA, Ramaswamy S, Jap BK; Science 1998;281:64-71. PMID:9651245

2: The 'Hinge' protein of cytochrome c reductase from potato lacks the acidic domain and has no cleavable presequence. Braun HP, Jansch L, Kurft V, Schmitz UK; FEBS Lett 1994;347:90-94. PMID:8013669