What is the state of the alpha subunit after it becomes inactive?

The alpha subunit of a G-protein becomes inactive after it hydrolyzes GTP (guanosine triphosphate) to GDP (guanosine diphosphate). In its active state, the alpha subunit is bound to GTP, which allows it to interact with various downstream effectors, like enzymes or ion channels, and propagate intracellular signals. Once GTP is hydrolyzed to GDP, the alpha subunit undergoes a conformational change that reduces its affinity for the effector proteins and enhances its affinity for the beta and gamma subunits of the G-protein complex. This transition effectively deactivates the alpha subunit, leading to a cessation of the signaling cascade that was initiated when it was active.

Thus, after the alpha subunit becomes inactive, it is indeed in an inactive state, characterized by its binding to GDP rather than GTP. This is crucial for the regulation of signal transduction pathways, ensuring that the signaling is tightly controlled and only active when necessary.