Respiratory electron transport chain (ETC)

The respiratory electron transport chain (ETC) is a critical metabolic system located within the inner mitochondrial membrane, consisting of a series of protein complexes (Complexes I-IV) and mobile electron carriers like ubiquinone and cytochrome c (StatPearls, 'Physiology, Mitochondrial Electron Transport Chain', 2023). Its primary biological function is to facilitate the transfer of electrons from donors such as NADH and FADH2 to a terminal electron acceptor, molecular oxygen, while simultaneously pumping protons across the membrane to create an electrochemical gradient. This gradient drives ATP synthase to produce the cellular energy currency, ATP, through oxidative phosphorylation. Dysfunction of the ETC is a hallmark of mitochondrial diseases like MELAS and is heavily implicated in the pathogenesis of Parkinson's disease and other neurodegenerative conditions (NIH, 'Mitochondrial Diseases', 2022). In therapy, the ETC is targeted by various agents: Metformin inhibits Complex I to improve insulin sensitivity, whereas drugs like Atovaquone target Complex III to treat parasitic infections; however, many ETC inhibitors are highly potent toxins, such as cyanide and carbon monoxide, which cause rapid death by arresting cellular respiration (PubChem, 'Cyanide', 2024).

Other names

Electron transport chainMitochondrial respiratory chainOxidative phosphorylation systemRespiratory electron transport systemOXPHOS

Drugs targeting the respiratory electron transport chain typically act by inhibiting specific enzyme complexes (I through IV), which halts the flow of electrons and disrupts the maintenance of the transmembrane proton gradient (StatPearls, 2023). This inhibition prevents the phosphorylation of ADP into ATP by ATP synthase (Complex V). Some compounds may also act as uncouplers, dissipating the proton motive force without inhibiting electron flow, or by increasing the production of reactive oxygen species (ROS) to induce cell death in targeted tissues such as tumors.