In the electron transfer system, it has been mentioned in prior questions that complexes I, III, and IV are proton pumps and that these pumps pump protons from the matrix into the intermembrane space.

My question.

  • However, where are the protons in the matrix supplied from?
  • In other words, where does the OH- generated when the protons are generated in the matrix disappear?
  • Why is it not biased to the alkaline side to the extreme even though the number of proton is decreasing rapidly due to being pumped out or used to dispose of surplus electrons?

In particular, it seems that the Protons in the matrix are used to dispose of surplus electrons in the electron transfer system by combining with externally introduced O2 to produce H2O, but this seems to result in too much OH-. I would like to know the fate of the excess alkali.

See also,

  • $\begingroup$ What "H2" are you referring to? Are you familiar with pH and dissociation of water into OH- and H+ (or H3O+)? $\endgroup$
    – Bryan Krause
    Sep 28, 2023 at 18:43
  • $\begingroup$ That typ. You're right, it's a proton. $\endgroup$ Sep 28, 2023 at 18:49
  • $\begingroup$ I know that there exists a chemical equilibrium in which the ionization product is constant. Both H+ and OH- should be produced in the process. And if the H+ produced is pumped out, the OH will be left behind. The protons may be used to dispose of the excess electrons, but in that case they will combine with externally introduced O2 instead of OH-. So there is even more OH- left over. In the process, it is likely that there will be more and more OH- only. $\endgroup$ Sep 28, 2023 at 18:53
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    $\begingroup$ I'm a bit unclear which part it is you're exactly trying to understand...is it that you're wondering where the "H+" comes from that combines with O2 to make H2O? Or are you wondering about the H+ pumped through the membrane? $\endgroup$
    – Bryan Krause
    Sep 28, 2023 at 18:56
  • $\begingroup$ Fate? Nothing. There is nothing in chemistry, thermodynamics or Nature that says a cellular compartment cannot have a particular non-neutral pH. It remains alkaline until the pH gradient is used to make ATP. $\endgroup$
    – David
    Sep 28, 2023 at 19:33


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