Bacterial respiratory chain cytochrome c oxidase complex (Complex IV) (Complex IV)

The bacterial respiratory chain cytochrome c oxidase complex, also known as Complex IV or aa3-type cytochrome c oxidase, is a transmembrane enzyme complex in bacterial cytoplasmic membranes that serves as the terminal component of the electron transport chain. It receives electrons from cytochrome c (reduced by Complex III, the cytochrome bc1 complex) via its CuA center, transferring them through cytochrome a to the binuclear cytochrome a3-CuB center, where molecular oxygen is reduced to water using four electrons and four protons, while pumping additional protons across the membrane to generate an electrochemical gradient for ATP synthesis. This process is highly efficient, involving rapid four-electron reduction of oxygen without superoxide intermediates, facilitated by a unique tyrosine-histidine post-translational modification. In bacteria, the core catalytic subunits (e.g., Cox1, Cox2, Cox3 homologs) are often mitochondrially encoded in eukaryotes but nuclear or plasmid-encoded in prokaryotes, with assembly requiring chaperones and cofactors like hemes and copper. As a therapeutic target, it is exploited by inhibitors like cyanide, azide, and carbon monoxide, which bind the binuclear center to halt respiration, leading to bactericidal effects in infections, though mammalian mitochondrial homologs pose toxicity risks. Bacterial variants show diversity, fostering a family of heme-copper oxidases adapted to different environments.

Other names

Cytochrome c oxidaseComplex IVCOXaa3-type cytochrome c oxidaseOxygen reductaseHeme-copper terminal oxidase

Inhibition of electron transfer to oxygen, Binding to binuclear center (cytochrome a3-CuB), Blockade of proton pumping and respiration