Which of the following is not involved in generation of proton gradient?

Proton gradient : The inner mitochondrial membrane, as such, is impermeable to protons (H+) and hydroxyl ions (OH-). The transpo of electrons through ETC is coupled with the. translocation of protons (H+) across the inner mitochondrial membrane (coupling membrane) from the matrix to the intermembrane space. The pumping of protons results in an electrochemical . or proton gradient. This is due to the. accumulation of more H+ ions (low pH) on the outer side of the inner mitochondrial membrane than the inner side. The proton . gradient developed due to the electron flow in the respiratory chain is sufficient to result in the synthesis of ATP from ADP and Pi. Ref : Biochemistry by U. Satyanarayana 3rd edition Pgno : 229