Lemur Tyrosine Kinase 3 belongs to the protein kinase superfamily. Tyr protein kinase family.A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to a tyrosine residue in a protein. Tyrosine kinases are a subgroup of the larger class of protein kinases. Phosphorylation of proteins by kinases is an important mechanism in signal transduction for regulation of enzyme activity. Most tyrosine kinases have an associated protein tyrosine phosphatase.Tyrosine kinases are particularly important today because of their implications in the treatment of cancer. A mutation that causes certain tyrosine kinases to be constitutively active has been associated with several cancers. Imatinib (brand names Gleevec and Glivec) is a drug able to bind the catalytic cleft of these tyrosine kinases, inhibiting its activity.