What must happen to GTP after the alpha subunit activates its effector protein?

After the alpha subunit of a G-protein activates its effector protein, GTP must be converted to GDP and inorganic phosphate (Pᵢ) to turn off the activation signal. This conversion is critical because it allows the G-protein to return to its inactive state.

The activation of the effector protein typically leads to a physiological response, such as a change in enzyme activity or ion channel status. Once the response is initiated, it is important for the cell to ensure that the signaling process does not continue indefinitely. By hydrolyzing GTP to GDP and Pᵢ, the alpha subunit undergoes a conformational change that decreases its affinity for the effector protein, effectively shutting off the signaling pathway.

Moreover, this hydrolysis is part of the intrinsic GTPase activity of the alpha subunit, a fundamental process in cell signaling that regulates the duration and intensity of the signal. Thus, the conversion from GTP to GDP and Pᵢ not only acts as a switch but also ensures that cells can appropriately respond to changes in their environment.