Thymidine kinase (TK) (TK)

Human thymidine kinases are essential enzymes in the pyrimidine salvage pathway that catalyze the phosphorylation of thymidine to thymidine monophosphate (dTMP) (UniProt: P04183, O00142). The family consists of two main isoforms: the cytosolic Thymidine kinase 1 (TK1), which is cell-cycle dependent and highly expressed during the S-phase, and the mitochondrial Thymidine kinase 2 (TK2), which is constitutively expressed (PubMed: 29153501). TK1 serves as a sensitive biomarker for cell proliferation, with elevated serum levels often correlating with tumor aggressiveness and poor prognosis in various cancers (PubMed: 30263416). In therapeutic contexts, these kinases are exploited to activate nucleoside analog prodrugs, such as trifluridine and idoxuridine, into active metabolites that inhibit DNA synthesis (PubChem). Conversely, mutations in the TK2 gene are a primary cause of mitochondrial DNA depletion syndrome, highlighting its role in organelle genome stability (PubMed: 11331615). Understanding the distinct roles of these isoforms is crucial for developing targeted oncology treatments and managing potential toxicities related to nucleotide metabolism.

Other names

Thymidine kinase 1TK1Thymidine kinase 2TK2ATP:thymidine 5'-phosphotransferaseCytosolic thymidine kinaseMitochondrial thymidine kinase

Thymidine kinases catalyze the transfer of a gamma-phosphate group from ATP to the 5'-hydroxyl group of thymidine, producing thymidine monophosphate (dTMP) and ADP (UniProt: P04183). This reaction is the rate-limiting step of the pyrimidine salvage pathway, providing a source of nucleotides for DNA replication and repair independent of de novo synthesis (PubMed: 29153501). In the context of pharmacology, these enzymes also phosphorylate various nucleoside analog drugs, converting them into active nucleotide forms that can inhibit DNA polymerases or cause DNA chain termination (PubChem).