Thymidine kinase is an enzyme (EC 2.7.1.21) that converts the nucleoside thymidine to the substance thymidine 5'-phosphate. The phosphate group is donated by adenosine triphosphate (ATP), which is converted into adenosine diphosphate (ADP).

The enzyme occurs accross many lifeforms. It is most relevant in the treatment of particular viral infections, as viruses express specific TKs that can be targeted with medication (such as aciclovir) without interfering with household genes that catalyse similar reactions.

Attempts have been made to transfect tumor cells (e.g. gliomas) with TK to make them susceptible to chemotherapy with aciclovir.

Reference

• Nanda D, Vogels R, Havenga M, Avezaat CJ, Bout A, Smitt PS. Treatment of malignant gliomas with a replicating adenoviral vector expressing herpes simplex virus-thymidine kinase. Cancer Res 2001;61:8743-50. Fulltext. PMID 11751394.