cytochrome-c oxidase activity

Definition

Target type: molecularfunction

Catalysis of the reaction: 4 ferrocytochrome c + O2 + 4 H+ = 4 ferricytochrome c + 2 H2O. [RHEA:11436]

Cytochrome c oxidase (COX), also known as complex IV, is the terminal enzyme of the mitochondrial electron transport chain. It is responsible for catalyzing the reduction of molecular oxygen (O2) to water (H2O) while simultaneously oxidizing reduced cytochrome c, a heme protein. The energy released from this reaction is used to pump protons across the inner mitochondrial membrane, generating a proton gradient that drives ATP synthesis.

The molecular function of COX involves a complex series of electron transfer reactions between metal centers within the enzyme. The process begins with the binding of reduced cytochrome c to COX, delivering an electron to heme a. This electron is then passed through a series of metal centers: heme a3, CuB, and finally to molecular oxygen bound to heme a3.

The reduction of oxygen occurs in a stepwise manner. First, O2 is bound to the reduced heme a3 and CuB, forming a superoxide anion (O2-). Subsequently, four electrons are transferred from cytochrome c to the enzyme, reducing O2 to two molecules of water. This process involves several intermediate states, including peroxide and hydroxyl radicals.

The transfer of electrons from cytochrome c to oxygen is coupled to the pumping of protons from the mitochondrial matrix to the intermembrane space. This proton pumping is driven by the energy released from the oxidation-reduction reactions. The proton gradient established across the inner mitochondrial membrane is then used by ATP synthase to generate ATP, the main energy currency of the cell.

In summary, the molecular function of cytochrome c oxidase involves the following key steps:
1. Binding of reduced cytochrome c to COX.
2. Electron transfer from cytochrome c to heme a and subsequent transfer through the metal centers of the enzyme.
3. Reduction of oxygen to water.
4. Proton pumping across the inner mitochondrial membrane.
5. Generation of a proton gradient that drives ATP synthesis.'
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Proteins (3)

Compounds (7)