: The Krebs cycle enzymes are located in the mitochondrial matrix between the cristae (inner mitochondrial membrane) but the enzymes for the electron transport and coupled phosphorylation are firmly bound to the cristae. Hydrogen atoms or electrons released in Krebs cycle from different substrates pass through different electron carriers and ultimately react with oxygen (at the end of ETS) in the cytosol and form water molecules. Cytosol is the soluble fraction of cytoplasm remaining after all particles have been removed by centrifugation.