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Jens C. Skou was the first to describe an ion pump - an enzyme that gives directed transport of ions through a cell membrane: a fundamental mechanism in every living cell. The existence of several similar ion pumps has since been demonstrated.

The first ion pump discovered

 
 
Ion composition outside the cell differs from that inside. When e.g. a nerve is stimulated Na+ flows into the cell. The electrical potential arising across the membrane causes the nerve impulse to propagate itself along the nerve. The normal state is restored when Na+ has been pumped out and K+ pumped in.
 
 

Jens Skou discovered Na+, K+-ATPase - an enzyme that maintains the balance of sodium (Na+) and potassium (K+) ions in cells. Within cells, the concentration of Na+ ions is lower, and that of K+ ions higher, than in the surrounding fluid.

Na+, K+-ATPase and other ion pumps must work all the time in our body. If they were to stop, our cells would swell up, and might even burst, and we would rapidly lose consciousness. A great deal of energy is needed to drive ion pumps - in humans, about 1/3 of the ATP that the body produces.

 

Na+, K+-ATPase cycles between two states
- open to the inside or the outside of the cell

 
 
The enzyme opens up towards the inside of the cell and exposes binding sites for three Na+ ions. When the ions are bound, an ATP molecule binds to the enzyme and one of its phosphate groups is transferred. The enzyme changes shape, opening towards the outside and the Na+ ions are released. Now binding sites for two K+ ions are exposed.
 
 
When K+ ions have been pumped into the cell the enzyme returns to its original state, ready to receive new Na+ ions.

When the K+ ions are bound, the phosphate group is released.
 
 
 

Ion pumps and pharmaceuticals

Ion pumps are affected by chemical substances. Digitalis plants contain a substance that inhibits Na+, K+-ATPase which results in an accumulation of sodium ions in cells. Used as a pharmaceutical, it causes reinforced heart muscle activity. Modern medicines against stomach ulcers suppress the activity of an ion pump that creates an acidic environment in the stomach.

 

 


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