The Sodium-potassium Pump Flashcards
Why is the sodium potassium pump important?
It generates a concentration gradient between cells and their environment. The pump moves 3 positively charged ions out for every 2 it pumps in. The potential difference that is created is essential for the generation of the resting potential in nerve cells. Some chemicals, such as digoxin from the foxglove, are inhibitors of the sodium-potassium pump. These chemicals act as potent toxins but can also have medicinal uses at very low concentrations.
What is the sodium-potassium pump? (Na+K+ATPase)
A vital transmembrane protein ATPase commonly found in animal cells. The pump moves sodium ions (Na+) put of cells and potassium ions (K+) into cells against steep concentration gradients.
What are the two stable conformational stages?
One has a high affinity for intracellular Na+ and the other a high affinity for extra cellular K+.
What happens in stage one?
In one conformational state, the sodium-potassium pump has a high affinity for Na+ ions. It exposes 3 Na+ binding sites to the cytosol. Three more Na+ move in and bind to these sites.
What happens in stage 2?
When the three Na+ are attached, the protein is able to hydrolyse an ATP molecule to ADP and phosphate. (This is why the protein is classified as an ATPase). The phosphate is not liberated into the cytosol as this stage, but is bonded to part of the protein. This phosphorylation causes a conformational change to the protein.
What happens in stage 3?
The second conformation has a lower affinity for Na+ ions but it can only release the Na+ ions to to the extra cellular fluid, thus pumping the three Na+ out the cell.
What happens in stage 4?
The second conformation has a higher affinity for K+ ions so K+ from the extracellular fluid attach to the two K+ binding sites? This triggers the release of the phosphate group from the protein.
What happens in stage 5?
The dephosphorylation restores the protein to its original conformation.
What happens in stage 6?
The original conformation has a low affinity for K+ so it releases the two K+ into the cell. The proteins affinity for Na+ is high again and so the cycle repeats.
