Coenzyme Q–cytochrome c reductase (Complex III)

Coenzyme Q–cytochrome c reductase (Complex III) is a multi-subunit enzyme complex embedded in the inner mitochondrial membrane that catalyzes the transfer of electrons from ubiquinol (CoQH2) to cytochrome c via the Q-cycle, coupling this transfer to proton translocation from the mitochondrial matrix to the intermembrane space. This process creates the electrochemical gradient necessary for ATP synthesis by ATP synthase (Complex V). Complex III consists of cytochrome b (encoded by mtDNA), cytochrome c1, Rieske iron-sulfur protein, and at least eight additional subunits. Dysfunction or inhibition of Complex III impairs cellular energy production, increases ROS generation, and triggers apoptosis or cell stress responses. Mutations in its subunits, especially cytochrome b, are associated with mitochondrial diseases. Complex III is a target for research drugs that explore mechanisms of cell death, oxidative stress, and metabolism, but interference in its function carries risks of toxicity and systemic mitochondrial dysfunction.

Other names

Cytochrome bc1 complexCoQ–cytochrome c reductaseUbiquinol–cytochrome c oxidoreductaseCIIIMitochondrial complex III

Inhibition of electron transfer (prevents Q-cycle, collapses proton gradient); Disruption of ATP synthesis (by blocking proton pumping); Induction of mitochondrial ROS (leading to cell apoptosis or stress response)