Protein phosphorylation, which plays a key role in most cellular activities, is a reversible process mediated by protein kinases and phosphoprotein phosphatases. Protein kinases catalyse the transfer of the gamma phosphate from nucleotide triphosphates (often ATP) to one or more amino acid residues in a protein substrate side chain, resulting in a conformational change affecting protein function. Phosphoprotein phosphatases catalyse the reverse process. Protein kinases fall into three broad classes, characterised with respect to substrate specificity [1]; Serine/threonine-protein kinases, tyrosine-protein kinases, and dual specificity protein kinases (e.g. MEK - phosphorylates both Thr and Tyr on target proteins). This entry represents the catalytic domain found in a number of serine/threonine- and tyrosine-protein kinases. It does not include the catalytic domain of dual specificity kinases.

1: The protein kinase family: conserved features and deduced phylogeny of the catalytic domains. Hanks SK, Quinn AM, Hunter T; Science. 1988;241:42-52. PMID:3291115

2: Protein kinase catalytic domain sequence database: identification of conserved features of primary structure and classification of family members. Hanks SK, Quinn AM; Methods Enzymol 1991;200:38-62. PMID:1956325

3: Protein kinases 6. The eukaryotic protein kinase superfamily: kinase (catalytic) domain structure and classification. Hanks SK, Hunter T; FASEB J 1995;9:576-596. PMID:7768349

4: The protein kinases of budding yeast: six score and more. Hunter T, Plowman GD; Trends Biochem Sci 1997;22:18-22. PMID:9020587