Cytochrome C Oxidase

I.U.B.: 1.9.3.1

C.A.S.:9001-16-5

Cytochrome c oxidase (EC 1.9.3.1), the terminal enzyme in the respiratory chain, catalyzes the four-electron reduction of molecular oxygen and couples this reaction to the generation of a proton gradient across the mitochondrial inner membrane.

The enzyme activity is associated with a protein lipid complex containing two dissimilar heme-copper catalytic centers (heme Aa + CuA and heme Aa₃ + CuB) combined with a number of other subunits. Some of the subunits are synthesized in the mitochondria while others are synthesized in the cytosol and imported into the mitochondria. The roles of the various subunits and the question of which subunits are essential to activity have received much attention.

Stability:

Stable as supplied for 12 months stored at -20°C. Dilutions at 0.05mg BCA protein per milliliter in 0.05M potassium phosphate, pH 6.8 containing 0.1% laurylmaltoside are stable for 24hr. stored at 2-8°C but significant losses occur at 25°C. The enzyme shows poor stability when diluted in water.

Unit Definition:

One Unit oxidizes one micromole of ferrocytochrome c per minute at 25°C, pH 6.8.