Complex II, also known as succinate dehydrogenase (SDH), is the second essential component of the electron transport chain (ETC) in oxidative phosphorylation. It is distinct as it is the only complex in the ETC that does not directly pump protons across the inner mitochondrial membrane, but instead plays a crucial role in the transfer of electrons from succinate to the mobile electron carrier, ubiquinone (Q). The electron transfer through Complex II generates a reduced form of ubiquinone (ubiquinol, QH2), which subsequently donates electrons to Complex III. Complex II receives electrons from succinate, a substrate generated in the TCA cycle. During the TCA cycle, succinate is converted to fumarate by succinate dehydrogenase. The same enzyme, succinate dehydrogenase, is also part of Complex II in the ETC and catalyses the reverse reaction, the oxidation of succinate to fumarate. During oxidation, two electrons and two protons are transferred from succinate to flavin adenine dinucleotide (FAD) within Complex II. FAD accepts electrons, becoming reduced to FADH2. The electrons are then transferred from FADH2 to a series of iron-sulphur (Fe-S) clusters within Complex II. The electrons from Complex II are subsequently transferred to ubiquinone (Q) within the inner mitochondrial membrane. The transfer of electrons from Complex II to ubiquinone reduces it to ubiquinol (QH2), the reduced form of Q. Unlike Complex I, which transfers electrons from NADH to ubiquinone and pumps protons across the membrane, Complex II does not pump protons. Instead, Complex II serves as a direct source of electrons to the ETC, transferring them to Complex III via ubiquinone. After Complex II reduces ubiquinone to ubiquinol, ubiquinol diffuses within the inner mitochondrial membrane and transfers its electrons to Complex III (cytochrome bc1 complex). Complex III is another important component of the ETC, and it facilitates the transfer of electrons from ubiquinol to cytochrome c, a small protein located in the intermembrane space of the mitochondria. Cytochrome c also serves as a mobile electron carrier, shuttling electrons between Complex III and Complex IV (cytochrome c oxidase). The transfer of electrons from cytochrome c to Complex IV results in the reduction of molecular oxygen (O2) to water (H2O) and drives the pumping of protons across the inner mitochondrial membrane. Succinate-linked respiration is a specific pathway of oxidative phosphorylation whereby electrons are directly transferred to Complex II through the oxidation of succinate. This pathway is essential for cells when energy demand is particularly high, and the TCA cycle is producing a surplus of succinate. Complex II plays a key role in succinate-linked respiration by accepting electrons from succinate and feeding them into the ETC for ATP synthesis. Complex II dysfunction has been implicated in tumour formation due to its role in succinate-linked respiration. Mutations in genes encoding subunits of Complex II or factors involved in its assembly can lead to altered electron transfer and succinate accumulation. High levels of succinate can subsequently inhibit enzymes involved in DNA methylation and histone modification, leading to epigenetic changes, thereby potentially promoting tumorigenesis. We offer a comprehensive product range of research tools for studying Complex II, including SDHB antibodies, and SDHA antibodies. Explore our full Complex II product range below and discover more, for less.