Protein kinase inhibitor
（重定向自Tyrosine kinase inhibitors）
A protein kinase inhibitor is a type of enzyme inhibitor that blocks the action of one or more protein kinases. Protein kinases are enzymes that add a phosphate (PO4) group to a protein, and can modulate its function.
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. There are also protein kinases that phosphorylate other amino acids, including histidine kinases that phosphorylate histidine residues.