Cytochrome c oxidase complex (COX or Complex IV)

Cytochrome c oxidase complex is a large multisubunit transmembrane enzyme found in mitochondria (and some prokaryotes), also known as **Complex IV** of the respiratory electron transport chain.[4][6] It catalyzes the final step of aerobic respiration by transferring electrons from reduced cytochrome c to molecular oxygen, reducing it to water while simultaneously pumping protons across the inner mitochondrial membrane—this process generates an electrochemical gradient essential for ATP synthesis via oxidative phosphorylation.[2][8] The human enzyme consists of 14 subunits with three core catalytic subunits encoded by mitochondrial DNA (MT‑CO1/COX I, MT‑CO2/COX II, MT‑CO3/COX III) and additional structural/regulatory subunits encoded by nuclear DNA.[4][6] Dysfunction or inhibition results in severe impairment of energy metabolism with broad clinical consequences ranging from acute toxicity (as seen with cyanide) to chronic degenerative disease states linked with inherited mutations or acquired defects.[1][8]

Other names

Complex IVCOXCytochrome c oxidaseMitochondrial complex IVElectron transport chain complex IV

Drugs targeting this molecule typically act as **enzyme inhibitors** by binding to the active site or regulatory sites, blocking electron transfer and halting cellular respiration, which can lead to chemical asphyxiation at the cellular level.[3]