Cytochrome c1 subunit of the cytochrome bc1 complex, an essential component of the respiratory electron transport chain required for ATP synthesis. The bc1 complex catalyzes the oxidation of menaquinol and the reduction of cytochrome c in the respiratory chain. The bc1 complex operates through a Q-cycle mechanism that couples electron transfer to generation of the proton gradient that drives ATP synthesis. a quinol + 2 Fe(III)-[cytochrome c](out) = a quinone + 2 Fe(II)-[cytochrome c](out) + 2 H(+)(out) The cytochrome bc1 complex is composed of a cytochrome b (QcrB), the Rieske iron-sulfur protein (QcrA) and a diheme cytochrome c (QcrC) subunit. The bc1 complex forms a supercomplex with cytochrome c oxidase (cytochrome aa3). Binds 2 heme c groups covalently per subunit. Cells lacking qcrCAB show strongly impaired growth in glucose minimal medium, which indicates that the bc1-aa3 pathway is the main route of respiration under these conditions. No stable monoheme protein can accumulate if the incorporation of the other heme group is blocked; assembly of both the cytochrome bc1 complex and the cytochrome bc1-aa3 supercomplex depends on heme assembly.