protein kinase n any of a class of allosteric enzymes that possess a catalytic subunit which transfers a phosphate from ATP to one or more amino acid residues (as serine, threonine, or tyrosine) in a protein's side chain resulting in a conformational change affecting protein function, that play a role in regulating intracellular processes, and that include many which are activated by the binding of a second messenger (as cyclic AMP)
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pro·tein ki·nase (proґtēn kiґnās) [EC 2.7.10–99] any of several groups of enzymes of the transferase class that catalyze the phosphorylation of serine, threonine, tyrosine, or histidine groups in enzymes and other proteins, using ATP as a phosphate donor. Specific protein kinases regulate by phosphorylation enzymes catalyzing key reactions in processes such as glycogen turnover, cholesterol biosynthesis, and amino acid transformations. Further subdivisions include protein-tyrosine kinases [EC 2.7.10], protein-serine/threonine kinases [EC 2.7.11], dual-specificity kinases [EC 2.7.12], and protein-histidine kinases [EC 2.7.13].Medical dictionary. 2011.