Sodium pump is an integral protein that fits perfectly within the lipid bilayer. The hydrophobic regions span across the membrane while the hydrophilic regions are extended outward to the aqeous extracellular phase. It is a tetrameric transmembrane protein which contains 4 subunits with 2 Alpha and 2 Beta subunits.The alpha subunits allow the binding of sodium ions and having a binding site for ATP to allow phosphorylation reaction occur (ATP is being hydrolysed into ADP and inorganic phosphate). The pump is an allosteric protein with 2 conformational changes while ions are bound on it .
- During the initial state, the sodium pump is opened, facing intracellular environment. This allows 3 Na+ ions bind on the inner surface of the pump, trigger the action of phosphorylation by using ATP. Conversion of ATP to ADP and inorganic phosphate.
- A conformational change for the pump and releases the 3 Na+ ions into extracellular environment.
- 2 K+ ions bind to the sodium pump, dephosphorylation occur and the conformational change is back to the initial state.
- The whole cycle will be repeated again.
Theory suggests that early cells lacked ion impermeable membranes and existed conditions with a high ratio of potassium to sodium. They were at equilibrium an of small ions with their surroundings and these ATPases developed as their surroundings changed. Therefore, these ATPases are an evolutionary method of maintaining the cellular ionic composition required for cellular functions.
- ↑ http://people.eku.edu/ritchisong/301notes2.htm
- ↑ Mulkidjanian, A. Y. et al. "Origin Of First Cells At Terrestrial, Anoxic Geothermal Fields". Proceedings of the National Academy of Sciences 109.14 (2012): E821-E830.