Editing Protein kinase (section)

==== Regulation ====
Ligand binding causes two reactions:
# [[Protein dimer|Dimer]]ization of two monomeric receptor kinases or stabilization of a loose dimer. Many ligands of receptor tyrosine kinases are [[valence (chemistry)|multivalent]]. Some tyrosine receptor kinases (e.g., the [[platelet-derived growth factor]] receptor) can form heterodimers with other similar but not identical kinases of the same subfamily, allowing a highly varied response to the extracellular signal.
# ''Trans''-autophosphorylation (phosphorylation by the other kinase in the dimer) of the kinase.

Autophosphorylation stabilizes the active conformation of the kinase domain. When several amino acids suitable for phosphorylation are present in the kinase domain (e.g., the insulin-like growth factor receptor), the activity of the kinase can increase with the number of phosphorylated amino acids; in this case, the first phosphorylation switches the kinase from "off" to "standby".