Coenzyme Q – cytochrome c reductase

Coenzyme Q – cytochrome c reductase, also known as cytochrome bc1 complex or complex III, is a crucial enzyme in the electron transport chain, playing a significant role in cellular respiration and energy production within the mitochondrion. This enzyme complex is involved in the mitochondrial electron transport chain, where it mediates the transfer of electrons from coenzyme Q10 (CoQ10) to cytochrome c. Its function is essential for the synthesis of adenosine triphosphate (ATP), the cell's main energy currency.

Structure and Function

The cytochrome bc1 complex is a multi-subunit complex that is embedded in the mitochondrial inner membrane. It consists of several protein subunits, including cytochromes b and c1, and the Rieske protein. The complex functions as a dimer, with each monomer facilitating the transfer of electrons. The transfer of electrons through the complex is coupled with the translocation of protons across the mitochondrial membrane, contributing to the proton gradient used by ATP synthase to generate ATP.

Mechanism

The mechanism of action of Coenzyme Q – cytochrome c reductase involves the Q cycle. In this cycle, CoQ10 is reduced to ubiquinol at the Qo site, which then donates electrons one at a time through the complex. This process results in the pumping of protons into the intermembrane space, creating a proton motive force. The electrons are finally transferred to cytochrome c, which carries them to Complex IV of the electron transport chain.

Clinical Significance

Mutations in the genes encoding the subunits of the cytochrome bc1 complex can lead to mitochondrial diseases and disorders. These conditions are characterized by impaired energy production and can affect various organs and tissues, particularly those with high energy demands such as the brain, muscle, and heart. Additionally, inhibitors of Coenzyme Q – cytochrome c reductase, such as antimycin A, are used in research to study the electron transport chain and mitochondrial function.

Pharmacological Inhibition

Certain compounds, including some pesticides and antibiotics, are known to inhibit the function of the cytochrome bc1 complex. This inhibition can lead to a decrease in ATP production and has been explored for therapeutic interventions in diseases related to mitochondrial dysfunction.

See Also

• Mitochondrion
• Electron transport chain
• Cellular respiration
• Coenzyme Q10
• Cytochrome c
• ATP synthase