The phosphate groups are usually added to serine, threonine, or tyrosine amino acids on the protein: most kinases act on both serine and threonine, the tyrosine kinases act on tyrosine, and a number (dual-specificity kinases) act on all three.
The phosphate groups are usually added to the serine, threonine, or tyrosine amino acid on the protein. Hence, protein kinase inhibitors can be subdivided or characterised by the amino acids whose phosphorylation is inhibited: most kinases act on both serine and threonine, the tyrosine kinases act on tyrosine, and a number (dual-specificity kinases) act on all three.