Abstract

The classical view of oxidative phosphorylation is that a proton motive force PMF generated by the respiratory chain complexes fuels ATP synthesis. Under glycolytic conditions, ATP synthase in its reverse mode also can contribute to the PMF. Here, we dissected the two functions of ATP synthase and the role of its inhibitory factor 1 (IF1) under different metabolic conditions in detail. pH profiles of mitochondrial sub-compartments were recorded with high spatial resolution in live mammalian cells by positioning a pH-sensor directly at F1 and FO of ATP synthase, complex IV and in the matrix. Our results clearly show that ATP synthase activity is substantially controlling the PMF and that IF1 is essential under OXPHOS conditions to prevent reverse ATP synthase activity due to an almost negligible {Delta}pH. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=183 SRC="FIGDIR/small/430746v2_ufig1.gif" ALT="Figure 1"> View larger version (50K): org.highwire.dtl.DTLVardef@1a975eforg.highwire.dtl.DTLVardef@7ddb49org.highwire.dtl.DTLVardef@c7a128org.highwire.dtl.DTLVardef@2559e8_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LIThe {Delta}pH along and across the inner mitochondrial membrane is not homogeneous C_LIO_LIThe proton motive force at cristae tips is controlled by F1 FO ATP synthase C_LIO_LIUnder OXPHOS conditions, the pH difference between FO and F1 of active ATP synthase is almost negligible (1.2 proton vs. 1 proton equivalent) C_LIO_LIIF1 is required to prevent the onset of ATP hydrolysis under OXPHOS conditions C_LI