SODIUM-POTASSIUM PUMP

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6 years ago

SODIUM-POTASSIUM PUMP

SODIUM-POTASSIUM PUMP/Na⁺-K⁺ ATPase/Na⁺-K⁺ PUMP:

Most important pump for primary active transport in body.

An Electrogenic pump.

– Responsible for maintaining Na⁺ & K⁺ conc. difference across cell membrane.

Mechanism:

ICF – High K⁺ concentration.

ECF – High Na⁺ concentration.

Both Na⁺ & K⁺ transported against concentration gradient.

Uses energy by hydrolyzing ATP;

– Pump contains ATPase activity.

Na⁺-K⁺ pump extrudes –

– 3 Na⁺out from cell.

– Pumps 2 K⁺ into cell.

Coupling ratio of Na⁺-K⁺pump – 3:2.

Structure:

Na⁺-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.

Na⁺ & 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 Na⁺.

– 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 Na⁺ concentration

– Thyroid hormones

– Aldosterone

– Insulin.

Factors inhibiting pump activity:

– CHF

– CKF

– Digoxin toxicity

– Dopamine.

Exam Important

SODIUM-POTASSIUM PUMP/Na⁺– K⁺ ATPase/Na⁺– K⁺ pump

Most important pump for primary active transport in body.

An Electrogenic pump.

Na⁺– K⁺pump extrudes –

– 3 Na⁺out from cell

– Pumps 2 K⁺ into cell

Coupling ratio of Na⁺– K⁺pump is 3:2.

Both Na⁺ & K⁺ are transported against concentration gradient.

Na⁺– K⁺pump uses energy by hydrolyzing ATP; this pump contain ATPase activity

Na⁺– K⁺pump – Carrier protein – Heterodimer

Na⁺– K⁺ transport occurs through α-subunits.

Intracellular portion of α-subunit has,

– Three Na⁺binding/receptor sites for Na⁺.

– 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.

Na⁺ – K⁺ pump 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.

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