Succinate Dehydrogenase: Difference between revisions

Succinate dehydrogenase (PDB = [[2wdv]] with empty ubiquinone binding site; PBD = [[1nek]] with ubiquinone bound), also called succinate-coenzyme Q reductase (SQR) or Complex II, is a tetrameric enzyme found in the cell membrane of some bacteria and the inner mitochondrial membrane of mammalian cells. It is classified as an α+β protein, as it contains segregated regions of α helices and antiparallel β sheets. It is involved in two aspects of digestion; it catalyzes the oxidation of succinate to fumarate in the citric acid cycle by simultaneously reducing ubiquinone to ubiquinol in the electron transport chain <ref>PMID:14672929</ref>.

The tetramer is composed of two hydrophilic and two hydrophobic subunits. The hydrophilic subunits are named SdhA and SdhB; the former is a flavoprotein containing a covalently-bound FAD cofactor a binding site for succinate, while the latter is Fe-S protein bearing the three iron-sulfur clusters 2Fe-2S, 3Fe-4S, and 4Fe-4S. The hydrophobic subunits, termed SdhC and SdhD, anchor the protein in the mitochondrial membrane and formally comprise cytochrome b <ref>PMID:12966066</ref> and <ref>PMID:12560550</ref>. This cytochrome contains six transmembrane α-helices, a heme b group, and a binding site for ubiquinone located in a space bounded by SdhB, SdhC, and SdhD <ref>PMID:12560550</ref> and <ref>PMID:16407191</ref>.