Kinases are enzymes responsible for catalyzing the transfer of phosphate between a wide variety of substrates. This process of adding a phosphate group is known as phosphorylation. In addition, kinases are cell signaling enzymes that play an important role regulating many cellular processes such as cell division, cell growth, gene expression, cell metabolism, apoptosis and cell cycle progression. An example would be tyrosine kinase enzymes. The tyrosine kinase enzyme catalyzes the transfer of a phosphate from ATP to the amino acid tyrosine on a substrate protein.