How many protons are pumped out per pair of electrons from NADH in oxidative phosphorylation? I have searched the web and found that 10 protons are suppose to get pumped out during the electron cycle, but i'm a bit confused. I'm trying to count, for every complex(1/3/4), the number of protons that are reduced in the matrix versus the number of protons added to the intermembrane space. The numbers don't add up. **my calculations:** * complex 1: 4 protons reduced, 4 protons added. * complex 3: 2 protons reduced, 4 protons added. * complex 4: 2 protons reduced(not counting the ones that condens to H2O), 2 protons added. ![oxidative phosphorylation electron chain](

It seems like the mistake is in complex III. Look at this image from here:

![electron transport system](

It clearly shows the number of protons reduced in (and taken from) matrix and number of protons pumped into inter-membrane space. So the data becomes:

**Complex I:**

_matrix:_ 2H+ reduced (from NADH + H+) + 2H+ pumped out

_IMS:_ 4H+ pumped in

**Complex II:**

_matrix:_ 2H+ reduced (from succinate)

_IMS:_ 0H+ pumped in

**Complex III:**

_matrix:_ 2H+ pumped out (when not considering complex II, you'd count 4H+ here)

_IMS:_ 4H+ pumped in (2 from complex II)

**Complex IV:**

_matrix:_ 2H+ reduced (to H2O, we won't consider it as you said) + 2H+ pumped out

_IMS:_ 2H+ pumped in

**TOTAL:**

_matrix:_ 10H+ subtracted/pumped out (with 2H+ to water, total 12H+)

_IMS:_ 10H+ pumped in

This satisfies your statement that "10 protons are supposed to get pumped out during the electron cycle". I Hope this helps ;)

`IMS = inter-membrane space`