1 Molecular Properties of Serum Thymidine Kinase 1 and Use of the Canine Enzyme in Disease Monitoring

Thymidine kinase 1 (ATP: thymidine 5'-phosphotransferase, EC 2.7.1.21, TK1) catalyzes the transfer of the gamma phosphate group from a phosphate donor to the 5´-hydroxyl group of thymidine to form thymidine monophosphate, which is converted to thymidine triphosphate and then utilized in DNA synthesis. TK1 activity markedly increases in G1 and S phase of the cell cycle and is found mainly in dividing cells, but also in an extracellular form in the blood. Increased serum TK1 levels are considered as a sensitive and useful marker for cell proliferation and detection of malignancy in clinical medicine. The aim of this study was to investigate the molecular characteristics of canine thymidine kinase 1 and utilize several anti-TK1 antibodies to a better understanding its role in disease prognostics, risk assessment, and monitoring of cancer development. Study I was undertaken to clarify the structure of recombinant, cellular and serum TK1 in order to improve the usefulness of serum TK1 (STK1) as a proliferation biomarker in neoplastic diseases. Several forms of STK1 were observed with differen