Sodium-Potassium Pump

  • One very common pump and found in all the cells of the body is the sodium-potassium pump. This pump is made up of three protein molecules that span the cell membrane.
  • It has three intracellular sites that have a high affinity to sodium and two extracellular sites that have a high affinity to potassium.
  • It has also got ATPase activity i.e. it can act as an enzyme to hydrolyse one phosphate bond from an ATP molecule.
  • When both the sodium and potassium sites are full, the ATPase is activiated and splits an ATP molecule into ADP, Phosphate group and energy.
  • The energy is utilised to bring about a conformational change in the proteins whereas the sodium sites project into the extracellular space and the potassium sites are presented into the intracellular space. At the same time the energy releases these ions.
  • Thus this pump, removes three sodium ions from the intracellular space and exchanges them to two potassium ions.
  • This pump serves at least four purposes:
  1. Due to the large number of sodium/potassium pumps in the body, it serves to regulate the metabolic rate of the individual especially through the thyropid hormone.
  2. produces a steep sodium gradient used to provide energy for the "coupled transport" of other molecules.
  3. The sodium/potassium gradient across the membrane is partially responsible for the electrochemical potential across nerve and muscle membranes.
  4. The extrsuion of sodium is important to reduce the osmotic inflow of water into the cell.