What type of receptor possesses enzymatic activity upon activation?

Enzyme-linked receptors, as the name suggests, possess intrinsic enzymatic activity upon activation. When a ligand binds to the extracellular domain of these receptors, it triggers a conformational change that activates the enzymatic function, typically initiating a phosphorylation cascade within the cell. This activation often leads to the phosphorylation of specific tyrosine residues on the receptor itself or on downstream substrates, which is crucial for signal transduction pathways associated with various cellular responses.

In the context of the other types of receptors, G protein-coupled receptors, while they do engage in signaling pathways that involve enzymes, do not have enzymatic activity themselves. Instead, they activate G proteins that subsequently interact with other enzymes. Ion channel receptors also do not possess enzymatic functions but instead facilitate the movement of ions across the cell membrane in response to ligand binding. Tyrosine kinase receptors are a subset of enzyme-linked receptors that specifically phosphorylate tyrosine residues but are essentially a specific type rather than the overarching category of enzyme-linked receptors. Thus, enzyme-linked receptors encompass a broader range of mechanisms and include other forms of enzymatic activity beyond just tyrosine phosphorylation.