![]() F 1F O ATP synthase consists of subcomplex F O, which is the proton pump located in the membrane, and subcomplex F 1, which is hydrophilic and extends into the matrix. While the primary proton pumps of the respiratory chain are localized in cristae sheets, rows of dimers of F 1F O ATP synthase line up along the cristae rims (Gilkerson et al, 2003 Vogel et al, 2006 Davies et al, 2011, 2012 Blum et al, 2019). Foremost, the Δ p drives ATP synthesis, coupling the oxidative steps of the respiratory complexes to ADP phosphorylation by F 1F O ATP synthase in a process known as oxidative phosphorylation (OXPHOS). The PMF, as defined by Peter Mitchell (Mitchell, 1961, 1966 Mitchell & Moyle, 1967) in his chemiosmotic theory, is Δ p (Δ p = ΔµH +/F F = Faraday constant), where Δ p consists of an electric (ΔΨ m) and a chemical part (ΔpH m): Δ p = ΔΨ m −2.3RT/F ΔpH (mV). The PMF then drives ATP synthesis by ATP synthase (CV). Thereby, this pumping generates a proton motive force (PMF), which is the transmembrane difference of the electrochemical potential of protons (ΔμH +). The redox activity of CI, CIII, and CIV is coupled to proton pumping from the matrix to the intracristal space (ICS). From there, cytochrome c delivers the electrons to CIV (cytochrome c oxidase), the final electron acceptor of the electron transport chain (ETC). During this process, the respiratory complexes CI (NADH dehydrogenase, NADH : ubiquinone oxidoreductase) and CII (succinate dehydrogenase) deliver electrons to CIII (cytochrome c reductase, coenzyme Q: cytochrome c–oxidoreductase). Under respiratory conditions, ATP is synthesized in process known as oxidative phosphorylation (OXPHOS). The extent to which ATP synthase activity contributes to this heterogeneity is poorly understood. Recent insights into the proton motive force (PMF) that drives ATP synthesis reveal a local and highly dynamic heterogeneity of PMF (Rieger et al, 2014 Sjoholm et al, 2017 Wolf et al, 2019 Toth et al, 2020). However, while the mechanisms by which ATP is produced have long been known, questions remain about a key regulatory step in the ATP synthesis process. Mitochondria are cellular power plants that are the major source of ATP under respiratory conditions. ![]()
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