Receptors with intrinsic enzymatic activity are the second biggest group of receptors after the GPCRs. They include four types according to the form of enzymatic activity of the intracellular domain (Figure 23a).
- Receptor tyrosine kinases (RTKs) On activation, the kinase domain phosphorylates tyrosine amino acid residues. There are seven classes of RTK with different extracellular domains (Figure 23b).
- Receptor serine–threonine kinases On activation, the kinase domain phosphorylates serine and/or threonine amino acid residues.
- Receptor tyrosine phosphatases The intrinsic tyrosine phosphatase activity of the enzymatic domain is suppressed on activation.
- Receptor guanylyl cyclases The enzymatic domain generates the second messenger cGMP from GTP following activation.