Component of the respiratory Qrc complex, that catalyzes the reduction of the menaquinone pool using electrons transferred from the reduced periplasmic cytochrome c3, and which is probably involved in sulfate respiration. Is likely essential for growth on H(2) or formate since the periplasmic hydrogenases and/or formate dehydrogenases act as primary electron donors for the Qrc complex. QrcC is an electron-transferring subunit; its cubane iron sulfur clusters form a pathway for electron transfer between the hemes of QrcA and the membrane quinone pool. Binds 3 [4Fe-4S] cluster per subunit. Binds 1 [3Fe-4S] cluster per subunit. kcat is 16.6 min(-1). Values are measured with the whole Qrc complex. The Qrc complex is composed of four subunits: QrcA, QrcB, QrcC and QrcD (PubMed:20498375). Can form a supercomplex with the [NiFe] hydrogenase HynA1 and the tetraheme Type I cytochrome c3 TpIc(3), its physiological electron donors (PubMed:21651911).