Coenzyme Q-cytochrome c reductase (Complex III) (Complex III)

Coenzyme Q-cytochrome c reductase, also known as Complex III or the cytochrome bc1 complex, is a multi-subunit enzyme located in the inner mitochondrial membrane [1, 2]. It is a critical component of the mitochondrial electron transport chain, where it facilitates the transfer of electrons from ubiquinol to cytochrome c while simultaneously pumping protons into the intermembrane space to drive ATP synthesis [2, 3]. Beyond energy production, Complex III is a significant source of reactive oxygen species (ROS), making it a key player in cellular redox signaling and oxidative stress [1, 12]. Mutations in its subunits are linked to various mitochondrial disorders, such as exercise intolerance and encephalomyopathies, and its dysfunction is implicated in neurodegenerative diseases and cancer [1, 17]. Pharmacologically, it is the primary target of the antimalarial drug atovaquone, which inhibits the enzyme's Qo site in parasites, and it is also a site of action for various research inhibitors and mitochondrial-targeted antioxidants [2, 9, 14].

Other names

Complex IIICytochrome bc1 complexUbiquinol-cytochrome c reductaseUbiquinone-cytochrome c oxidoreductaseMitochondrial respiratory chain complex IIICIIIUbiquinol:ferricytochrome-c oxidoreductase

Inhibition of electron transfer at the Qo or Qi binding sites of the cytochrome bc1 complex, leading to the collapse of the mitochondrial membrane potential and inhibition of ATP synthesis, or the restoration of electron transport chain function through substrate supplementation [1, 2, 10].