Sodium as Primary and Secondary Coupling Ion in Bacterial Energetics
Primary coupling ion – ion whose transmembrane electrochemical gradient could directly be generated at the expense of the external energy source and used to perform chemical (ATP synthesis), osmotic (active transport), or mechanical (motility) work. Secondary coupling ion – can be actively transported across the membrane only at the expense of the transmembrane electrochemical gradient of the primary coupling ion.
Perhaps the most prominent biological role of sodium-binding/transporting proteins is their involvement into the transformation of energy in biomembranes. All mitochondria and chloroplasts, as well as most bacteria on our planet, transform a plethora of available external energy sources into the transmembrane electrochemical gradient of H+ ions (proton-motive force, or PMF). The PMFcould be directly used to drive a variety of endergonic processes, such...