Question

Sodium potassium ATPase is comprised of

• A. 2 alpha and 3 beta units
• B. 2 alpha and 2 beta units
• C. 1 alpha and 2 beta units
• D. 1 alpha and 1 beta unit

Hint:

The catalytic work of the pump (ATP hydrolysis, ion binding) is performed entirely by the alpha ($\alpha$) subunit.
The beta ($\beta$) subunit acts as a molecular chaperone that ensures the newly synthesized alpha subunit is delivered safely to the plasma membrane.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The sodium-potassium pump ($\text{Na}^+/\text{K}^+$-ATPase) is a vital transmembrane P-type ATPase found in the plasma membrane of all animal cells.
It actively pumps three sodium ions ($\text{Na}^+$) out of the cell and imports two potassium ions ($\text{K}^+$) into the cell against their electrochemical gradients, utilizing the energy from one ATP molecule.

Step 2: Detailed Explanation:
Biochemically, the functional $\text{Na}^+/\text{K}^+$-ATPase is a oligomeric transmembrane glycoprotein.
In its physiological, functional state in mammalian membranes, it exists as a tetrameric complex composed of:
- Two alpha ($\alpha$) subunits: The $\alpha$ subunit ($\approx 112\,\text{kDa}$) is the catalytic subunit. It contains the binding sites for ATP, $\text{Na}^+$, $\text{K}^+$, and cardiotonic steroids like ouabain.
- Two beta ($\beta$) subunits: The $\beta$ subunit ($\approx 35\,\text{kDa}$) is a heavily glycosylated polypeptide required for the proper folding, membrane targeting, and stabilization of the catalytic $\alpha$ subunits.
Thus, the structurally complete, functional enzyme complex is represented by a $(\alpha\beta)_2$ stoichiometry, meaning it comprises 2 alpha and 2 beta subunits.

Step 3: Final Answer:
Therefore, the sodium-potassium ATPase is comprised of 2 alpha and 2 beta subunits, which corresponds to option (B).