Figure 1

A protonic biotransducer controlling ATP synthesis in mitochondria. Mitochondria synthesize ATP molecules using the proton-motive force, which is generated by a proton (H⁺) concentration gradient and a voltage gradient. Protons are pumped from the exoplasmic face to the cytosolic face, creating a proton concentration gradient (H⁺_{exoplasmic face} > H⁺_{cytosolic face}) and a voltage gradient (positive at the cytosolic face and negative at the exoplasmic face) across the membrane. During ATP synthesis, protons flow in the reverse direction through ATP synthase. When the SPA pH modulator transfers H⁺ between the solution and contact, it changes the pH around the SPA microelectrodes. This pH modulation couples to the mitochondrial proton-motive force. (a) Proton-motive force (H⁺ concentration in intermembrane space) decreases upon an applied reduced potential to the SPA contact. (b) Proton-motive force increases upon an applied oxidizing potential to the SPA contact, resulting in mitochondrial ATP synthesis.