Accepts electrons from ETF and reduces ubiquinone. a ubiquinone + reduced [electron-transfer flavoprotein] = a ubiquinol + H(+) + oxidized [electron-transfer flavoprotein] Binds 1 [4Fe-4S] cluster. Displays higher growth rate and higher sensitivity to superoxide and heat stress, on nonfermentable carbon sources. Leads to decreased intracellular oxidation upon heat shock. Present with 3320 molecules/cell in log phase SD medium. Belongs to the ETF-QO/FixC family.