Puzzling subunits of mitochondrial cytochrome reductase

The ubiquinol-cytochrome c reductase complex, like the other
proton-pumping respiratory complexes of mitochondria, is an
assembly of many different subunits. However, only a few of these
subunits participate directly in the electron transfer and proton
translocation. The roles of the other subunits are largely unknown.
We discuss here some intriguing features of two of these subunits.