Iron—cytochrome-c reductase

Iron—cytochrome-c reductase, also known as complex III or the cytochrome bc1 complex, is a crucial enzyme in the electron transport chain, playing a vital role in cellular respiration and energy production within the mitochondrion. This enzyme facilitates the transfer of electrons from ubiquinol (QH2) to cytochrome c, a process that is essential for the synthesis of adenosine triphosphate (ATP), the energy currency of the cell.

Structure and Function

Iron—cytochrome-c reductase is a multi-subunit complex embedded in the mitochondrial inner membrane. It consists of several protein subunits, including cytochromes b and c1, and the Rieske protein. The complex operates through the Q-cycle, a mechanism that efficiently transfers electrons and contributes to the generation of a proton gradient across the mitochondrial membrane. This proton gradient is then used by ATP synthase to produce ATP.

The activity of iron—cytochrome-c reductase is regulated by the availability of its substrates, ubiquinol and cytochrome c, and is influenced by the proton motive force across the mitochondrial membrane. Inhibitors of this complex, such as antimycin A, can disrupt cellular respiration and ATP production, highlighting the enzyme's critical role in metabolic processes.

Clinical Significance

Dysfunction of iron—cytochrome-c reductase can lead to a variety of mitochondrial diseases, as it impairs the cell's ability to produce ATP efficiently. Mutations in genes encoding the subunits of the complex or factors involved in its assembly can result in diseases such as Leigh syndrome and mitochondrial complex III deficiency, which are characterized by a wide range of symptoms, including neurodegeneration, muscle weakness, and organ failure.

Research into iron—cytochrome-c reductase has also provided insights into the mechanisms of apoptosis (programmed cell death) and the development of drugs that can target the electron transport chain in cancer cells, offering potential therapeutic strategies for cancer treatment.

See Also

• Electron transport chain
• Mitochondrial disease
• Cellular respiration
• Ubiquinone
• Cytochrome c