What does the activated receptor increase the affinity of the alpha subunit for?

The activated receptor increases the affinity of the alpha subunit for GTP. This process is crucial in the signaling pathway involving G protein-coupled receptors (GPCRs). When a ligand binds to the receptor, it induces a conformational change that activates the associated G protein.

In its inactive state, the alpha subunit of the G protein is bound to GDP. The activation of the receptor promotes the exchange of GDP for GTP on the alpha subunit. This exchange is a key step in signal transduction, as GTP-bound alpha subunits can interact with various downstream effectors, leading to cellular responses. The affinity for GTP is much higher than that for GDP once the receptor is activated, facilitating the signal's propagation within the cell.

By increasing this affinity, the activated receptor effectively ensures that the G protein can transition from an inactive state (bound to GDP) to an active state (bound to GTP), thereby amplifying the signal initiated by the original binding of the ligand to the receptor.