According to Sazanov (2015), "to reduce oxygen to water, four 'chemical' protons are taken from the matrix side [...]. In addition, four protons are pumped across the membrane into the IMS". A similar statement is made in the review by Vercellino & Sazanov (2022, pp. 152–3).
How is this compatible with only 10 protons being pumped into the IMS in total and only 2 by Complex IV (see also How many protons are pumped out per pair of electrons from NADH in oxidative phosphorylation?)? Does the number of 10 perhaps simply result from the assumption of a 10/3 H+/ATP ratio? What am I missing here? 😅
(the literature on H+/2e- stoichiometry, if anything, added to my confusion)
