Thymidine kinase

Thymidine kinase (TK) is an enzyme that is found in most living organisms. It plays a crucial role in the DNA replication process, as it is responsible for the phosphorylation of thymidine, a nucleoside that is one of the building blocks of DNA.

Function

Thymidine kinase catalyzes the transfer of a phosphate group from adenosine triphosphate (ATP) to thymidine, producing thymidine monophosphate (TMP) and adenosine diphosphate (ADP). This reaction is a key step in the salvage pathway, a method of recycling nucleosides produced during DNA replication and repair.

Structure

Thymidine kinase exists in two forms: TK1 and TK2. TK1 is a cytosolic enzyme that is active during the S phase of the cell cycle, while TK2 is a mitochondrial enzyme that is active throughout the cell cycle. Both forms of the enzyme are homodimers, meaning they consist of two identical subunits.

Clinical significance

Thymidine kinase is a target for antiviral drugs, such as acyclovir, which is used to treat herpes simplex virus infections. The enzyme is also a useful biomarker for certain types of cancer, as its activity is often elevated in cancer cells.

See also

• DNA replication
• Nucleoside
• Phosphate group
• Adenosine triphosphate
• Thymidine monophosphate
• Adenosine diphosphate
• Salvage pathway
• Cell cycle
• Herpes simplex virus
• Biomarker
• Cancer

Cell biology