“…E. coli uses both protons and sodium ions as coupling ions for the uptake of sugars, amino acids and other nutrients [e.g., lactose-H + (LacY), galactose-H + (GalP), arabinose-H + (AraE), xylose-H + (XylE), proline-H + (ProP), proline-Na + (PutP), serine-Na +, glutamate-Na + (GItS), glutamate-H + (GltP), a-ketoglutarate-H + (KgtP), pantothenate-Na + (PanF)] [11,16,[46][47][48][49][50][51]. Unique examples are the melibiose carrier (MelB) of E. coli and the alanine carrier protein (Acp) of thermophilic bacterium PS3 which can choose among protons and sodium ions for the uphill movement of solutes [13,52,53], and these may actually represent intermediate stages in the evolution from H + to Na ÷ energetics or vice versa.…”