Sodium-Potassium Pump
SODIUM-POTASSIUM PUMP/Na2+-K+ ATPase/Na2+-K+ PUMP:
- Most important pump for primary active transport in body.
- An Electrogenic pump.
- Responsible for maintaining Na2+ & K+ conc. difference across cell membrane.
Mechanism:
- ICF – High K+ concentration.
- ECF – High Na2+ concentration.
- Both Na2+ & K+ transported against concentration gradient.
Uses energy by hydrolyzing ATP;
- Pump contains ATPase activity.
- Na2+-K+ pump extrudes –
- 3 Na2+ out from cell.
- Pumps 2 K+ into cell.
- Coupling ratio of Na2+-K+pump – 3:2.
Structure:
- Na2+-K+pump-Carrier protein – Heterodimer.
- Made of two separate globular proteins:
- Larger α-subunit –
- Molecular weight -100,000
- Smaller β-subunit –
- Molecular weight – About 55,000.
- Na2+ & K+ transport occurs through α-subunits.
- Both α- & β- subunits span across membrane with an intracellular & extracellular site.
Sites of α-subunit:
- Intracellular site has,
- 3 Na2+binding/receptor sites for Na2+.
- An ATP binding site.
- A phosphorylating site.
- ATPase activity.
- Extracellular site has,
- 2 K+ binding/receptor sites for K+.
- An Ouabain binding site.
Sites of β-subunit:
- 3 extracellular glycosylation sites.
- All 3 attached carbohydrate residue.
FUNCTION:
- Acts as an electrogenic pump.
- Due to net movement of positive charge out of cell.
- Maintains intracellular fluid ionic composition.
- Maintains electrochemical potential difference across cell membrane.
- Contributes only 4 millivolts to total resting membrane potential of 90 volts which is almost negligible.
- Active transport of Na+ & K+ – One of major energy-using process in body.
- Average, energy utilized,
- In cell – Accounts about 24% of energy.
- In neurons – 70% of energy.
FACTORS INFLUENCING PUMP ACTIVITY:
Factors stimulating pump activity:
- Increased intracellular Na2+ concentration
- Thyroid hormones
- Aldosterone
- Insulin.
Factors inhibiting pump activity:
- CHF
- CKF
- Digoxin toxicity
- Dopamine.
Exam Question
SODIUM-POTASSIUM PUMP/Na2+– K+ ATPase/Na2+– K+ pump
- Most important pump for primary active transport in body.
- An Electrogenic pump.
- Na2+– K+ pump extrudes –
- 3 Na2+out from cell
- Pumps 2 K+ into cell
- Coupling ratio of Na2+– K+ pump is 3:2.
- Both Na2+ & K+ are transported against concentration gradient.
- Na2+– K+ pump uses energy by hydrolyzing ATP; this pump contain ATPase activity
- Na2+– K+ pump – Carrier protein – Heterodimer
- Na2+– K+ transport occurs through α-subunits.
- Intracellular portion of α-subunit has,
- Three Na2+ binding/receptor sites for Na2+.
- An ATP binding site.
- A phosphorylating site.
- ATPase activity.
- Extracellular portion has,
- Two K+ binding/receptor sites for K+.
- An Ouabain binding site.
- β-subunit has three extracellular glycosylation site.
- Na2+ – K+ pump contributes only 4 millivolts to total resting membrane potential of 90 volts which is almost negligible.
- Active transport of Na2+ & K+– One of major energy-using process in body.
Don’t Forget to Solve all the previous Year Question asked on Sodium-Potassium Pump
