In biochemistry, a kinase is a type of enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific substrates, a process referred to as phosphorylation. Kinases are part of the larger family of phosphotransferases. Kinases are not to be confused with phosphorylases, which carry out phosphorolysis, the breaking of a bond using an inorganic phosphate group; or with phosphatases, which remove phosphate groups.
One of the largest groups of kinases are protein kinases, which act on and modify the activity of specific proteins. Kinases are used extensively to transmit signals and control complex processes in cells. More than five hundred different kinases have been identified in humans. Their enormous diversity, as well as their role in signaling, makes them an object of study.
Various other kinases act on small molecules such as lipids, carbohydrates, amino acids, and nucleotides, either for signaling or to prime them for metabolic pathways. Kinases are often named after their substrates.
See also 
- Cyclin-dependent kinase
- Ca2+/calmodulin-dependent protein kinase
- Signal transduction
- G protein-coupled receptor