Complex IV

Complex IV (Cytochrome C Oxidase)

Overall Reaction: O2 + 4H+ + 4e- → 2H2O

Electrons are moved from cytochrome C onto oxygen which pumps 2H+ per electron pair.

Components: 

Heme groups: Heme A and Heme A3

3 Copper atoms: CuA/CuA and Copper B

Let's break this down…

Step One: Cytochrome C drops off its one e-. This e- travels its way down the system stopping at 

CuA/CuA, then Heme A, to Heme A3, and finally onto CuB

Step two: Another cytochrome C drops off its e-, and this follows the same path, but stops at the Heme A3 group. 

NOTE: Both of these are in their reduced states now!

Step three: These two complexes now bind O2 (One oxygen on the Heme A3, one on the CuB) which forms a peroxide bridge 

• NOTE: To help you remember the next step, I remember “peroxide” bridge as one hydrogen “per oxide” aka per oxygen! 

Step four: Two hydrogen atoms are brought in from the matrix and bind the each oxygen, breaking the bridge

Step five: 2 more hydrogen atoms are brought in from the matrix and form H2O, returning the CuB and Heme A3 to their normal state.