Ubiquinol-cytochrome c oxidoreductase (Mitochondrial bc1 complex) (Complex III)

The Mitochondrial bc1 complex, also known as Ubiquinol-cytochrome c oxidoreductase or Complex III, is a crucial multi-subunit enzyme embedded in the inner mitochondrial membrane. It plays a central role in the mitochondrial respiratory chain, facilitating electron transfer from ubiquinol to cytochrome c and coupling this process to proton translocation across the membrane, which is essential for ATP synthesis. Dysfunction of this complex is implicated in various diseases, including mitochondrial myopathies, neurodegenerative disorders like Parkinson's and Alzheimer's, and contributes to cellular aging. It is also a validated therapeutic target for a range of infectious diseases, including malaria and fungal infections, and is targeted by antibiotics, pesticides, and anti-parasitic drugs. Drugs often inhibit its function by disrupting the Q-cycle mechanism through binding to specific quinone-binding sites. However, targeting the bc1 complex can present challenges such as cytotoxicity and the development of drug resistance, and its activity can also lead to the generation of reactive oxygen species.

Other names

Cytochrome bc1 complexcyt bc1ubiquinol-cytochrome c reductasecytochrome c reductase

The Mitochondrial bc1 complex operates through a Q-cycle mechanism, coupling electron transfer to the generation of a proton gradient that drives ATP synthesis. Drugs targeting this complex typically inhibit its electron transfer function by binding to specific quinone-binding sites (QoI/QiI sites), thereby disrupting the Q-cycle. This inhibition can lead to a reduction in energy production and increased oxidative stress, or enhance the efficacy of other therapeutic agents.