Question

If membrane proteins could flip-flop across bilayer leaflets easily, how would the function of the transmembrane protein Na+/K+ ATPase (sodium-potassium pump) be affected? What will happen to the resting membrane potential?

Answer 1

Na+/K+ ATPase is an ATP driven pump. It works by pushing the ions against their concentration gradient. It has a binding pocket for ATP on the inner side of the membrane. This binding triggers the binding of Na+ ions to it. The ATP is hydrolyzed to form ADP and Pi. The energy released in the process brings about a conformational change in the protein thereby expelling Na+ outside. In turn, it binds to K+ ions present outside, and this binding triggers it to obtain the original conformation, thereby pulling K+ ions inside.

Now, if the membrane proteins could flip flop easily, the pump would be inverted. It would lead to the ATP binding site shifted outside and hence the pump will completely lose its function in this inverted state. However, it will continue it's function while the ATP side is on the inside.

This loss of function will lead to the accummulation of Na+ ions inside the cell. And as a result, the resting membrane potential will become more and more positive with time.