bio

Cytochrome c oxidase

The final enzyme of the respiratory chain - Complex IV - where the electrons stripped from food are handed to oxygen to make water. The whole business of breathing exists to serve this one step. Which is why it is the target of the fastest poisons known: cyanide and hydrogen sulfide both bind its iron core and stop the reaction. When it is blocked, oxygen is still in the blood and still reaching the cell, but the cell can no longer use it - suffocation from the inside, happening in every mitochondrion at once.