mitochondrial respiratory chain complex II, succinate dehydrogenase complex (ubiquinone)

Definition

Target type: cellularcomponent

A protein complex located in the mitochondrial inner membrane that forms part of the mitochondrial respiratory chain. Contains the four polypeptide subunits of succinate dehydrogenase, flavin-adenine dinucleotide and iron-sulfur. Catalyzes the oxidation of succinate by ubiquinone. Connects the TCA cycle with the respiratory chain. [GOC:mtg_sensu, GOC:vw, ISBN:0198547684]

The mitochondrial respiratory chain complex II, also known as succinate dehydrogenase complex (ubiquinone), is a crucial enzyme complex embedded in the inner mitochondrial membrane. It serves as a key player in both the citric acid cycle and the electron transport chain.

Complex II is unique among the respiratory chain complexes in that it directly interacts with both the mitochondrial matrix and the intermembrane space. It consists of four subunits:

* **SDHA (Succinate dehydrogenase flavoprotein subunit):** Located in the mitochondrial matrix, SDHA binds to the substrate succinate and contains a FAD prosthetic group that accepts electrons from succinate.
* **SDHB (Succinate dehydrogenase iron-sulfur protein subunit):** Located in the mitochondrial matrix, SDHB contains three iron-sulfur clusters (2Fe-2S and 4Fe-4S) that facilitate electron transfer.
* **SDHC (Succinate dehydrogenase cytochrome b560 subunit):** Located in the inner mitochondrial membrane, SDHC is a transmembrane protein with a heme b group that accepts electrons from the iron-sulfur clusters.
* **SDHD (Succinate dehydrogenase cytochrome b560 subunit):** Also located in the inner mitochondrial membrane, SDHD forms a dimer with SDHC and participates in electron transfer.

The catalytic mechanism of complex II involves the following steps:

1. **Succinate oxidation:** Succinate binds to SDHA and is oxidized to fumarate, transferring two electrons to the FAD prosthetic group.
2. **Electron transfer:** Electrons from FAD are passed to the iron-sulfur clusters in SDHB.
3. **Ubiquinone reduction:** Electrons from the iron-sulfur clusters are finally transferred to ubiquinone (Q) in the intermembrane space, reducing it to ubiquinol (QH2).

Complex II is essential for cellular respiration by linking the citric acid cycle to the electron transport chain. It contributes to the generation of a proton gradient across the inner mitochondrial membrane, which drives ATP synthesis. Additionally, complex II plays a role in the regulation of cellular metabolism and is implicated in various disease processes, including cancer and neurodegenerative disorders.'
"

Proteins (1)

Compounds (1)