Question

Explain how phosphorylation is involved in the function of the sodium- potassium ATPase.

Short answer

Phosphorylation alters the sodium-potassium ATPase shape to expel sodium ions. Dephosphorylation allows potassium ions to enter the cell, maintaining the electrochemical gradient.

Step-by-step solution

Understand the Sodium-Potassium ATPase

The sodium-potassium ATPase is an enzyme found in the plasma membrane of cells. It helps maintain the cell's electrochemical gradient by pumping three sodium ions out of the cell and two potassium ions into the cell using energy from ATP.

Role of ATP in the ATPase Function

The enzyme uses energy from ATP to change its shape and transfer ions across the cell membrane. ATP binds to the sodium-potassium ATPase and is hydrolyzed to ADP and an inorganic phosphate (Pi).

Phosphorylation

Phosphorylation refers to the addition of a phosphate group to a molecule. In the context of sodium-potassium ATPase, phosphorylation occurs when the Pi (from ATP hydrolysis) attaches to the enzyme, causing a conformational change.

Conformational Change Due to Phosphorylation

When the sodium-potassium ATPase is phosphorylated, it changes shape to move the three sodium ions out of the cell. This conformational change is essential for the enzyme’s function.

Dephosphorylation

After releasing the sodium ions outside the cell, the enzyme is dephosphorylated, causing another conformational change. This change allows two potassium ions to bind from the outside and be transported into the cell.

Overall Process Summary

In summary, phosphorylation and dephosphorylation of the sodium-potassium ATPase are crucial for its function. Phosphorylation causes the enzyme to expel sodium ions, and dephosphorylation enables it to bring in potassium ions, maintaining the electrochemical gradient essential for cellular functions.

Key concepts

Sodium-Potassium ATPase

The sodium-potassium ATPase is a critical enzyme found in the plasma membrane of many cells. Its main function is to maintain the cell’s electrochemical gradient. This gradient is vital for numerous cellular processes such as nerve impulse transmission and muscle contraction. The enzyme works by transporting three sodium ions out of the cell and bringing two potassium ions into the cell, against their concentration gradients. This transportation requires energy, which the enzyme obtains from ATP.

ATP Hydrolysis

ATP hydrolysis is the process of breaking down an ATP molecule into ADP (adenosine diphosphate) and an inorganic phosphate (Pi). This reaction releases energy. In the context of sodium-potassium ATPase, this energy is used to power the transport of sodium and potassium ions across the cell membrane. When ATP binds to the sodium-potassium ATPase, it is hydrolyzed, and the released energy drives the necessary conformational changes in the enzyme.

Conformational Change

A conformational change refers to a change in the shape or structure of an enzyme. For sodium-potassium ATPase, these changes are essential for its function. When ATP is hydrolyzed, and a phosphate group attaches (phosphorylation), the enzyme undergoes a conformational change that transports sodium ions out of the cell. Conversely, when the phosphate group is removed (dephosphorylation), the enzyme changes shape again, allowing potassium ions to be brought into the cell. These conformational changes are what enable the enzyme to move ions against their concentration gradients.

Phosphorylation

Phosphorylation involves the addition of a phosphate group to a molecule. For the sodium-potassium ATPase, phosphorylation happens when the inorganic phosphate (Pi) from ATP hydrolysis attaches to the enzyme. This event is crucial because it triggers a conformational change in the enzyme. When the enzyme changes its shape, it can transport three sodium ions from the inside of the cell to the outside. This step is imperative for the continued functioning of the enzyme and overall cellular activity.

Dephosphorylation

Dephosphorylation is the removal of a phosphate group from a molecule. For the sodium-potassium ATPase, this process occurs after the enzyme has transported sodium ions out of the cell. The removal of the phosphate group triggers another conformational change. This change is necessary for two potassium ions to bind to the enzyme from the outside of the cell. Once the potassium ions are bound, they are transported into the cell, completing the cycle of the enzyme’s function.

Electrochemical Gradient

An electrochemical gradient refers to a difference in the concentration of ions and electrical charge across a membrane. For cells, maintaining this gradient is crucial for various functions, including the generation of action potentials in neurons and muscle cells. The sodium-potassium ATPase plays a central role in maintaining this gradient by ensuring the correct distribution of sodium and potassium ions. By continuously pumping three sodium ions out of the cell and bringing two potassium ions in, the enzyme helps preserve the necessary conditions for numerous vital cellular processes.