The standard reduction potentials (E0) for three newly-discovered cytochromes, X, Y and Z in electron transport chain of a certain microorganism. These values are: Cytochrome X (ox) + 1 e- Cytochrome X (red): E0 = + 0.20 V Cytochrome Y (ox) + 1 e- Cytochrome Y (red): E0 = 0.30 V Cytochrome Z (ox) + 1 e- Cytochrome Z (red): E0 = + 0.06 V What is the sequence of electron transfer involving the three cytochromes above?
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Energy conversion is one of the fundamental processes supporting life of all organisms. It gives power to maintain homeostasis inside each cell and among cells. To achieve this, the process of energy conversion itself must be efficient, safe, and appropriately regulated. As the universal source of energy directly available for the cells to do useful work is stored in the concentrations of ATP, ADP, and Pi that are kept far from their equilibrium concentrations, the bioenergetic processes evolved to use the energy released from various chemical or physical processes to power the synthesis of ATP from ADP and Pi. While some amounts of ATP can be synthesized by water-soluble enzymes, the major fraction of ATP synthesis is associated with the operation of enzymes that are assembled to form specific bioenergetic paths (194). These enzymes are embedded in biological membranes involved in energy conversion (bioenergetic membranes). The factor that unifies a diversity of substrates used by these enzymes and a diversity of molecular mechanisms of conversion of these substrates is a proton-motive force (PMF), a central element of Peter Mitchell's chemiosmotic theory (176, 179). PMF depends on the difference of pH values over a bioenergetic membrane (ΔpH) and the membrane potential (ΔΨ; difference in electrical potentials between two aqueous compartments separated by a membrane). PMF, generated by the enzymes that use external source of energy to transfer protons between compartments separated by a bioenergetic membrane, forces ATP-synthase to convert ADP and Pi into ATP.