Phosphorylates thymidine, deoxycytidine, and deoxyuridine in the mitochondrial matrix (PubMed:9989599, PubMed:11687801). In non-replicating cells, where cytosolic dNTP synthesis is down-regulated, mtDNA synthesis depends solely on TK2 and DGUOK (PubMed:9989599). Widely used as target of antiviral and chemotherapeutic agents (PubMed:9989599). ATP + thymidine = ADP + dTMP + H(+) 2'-deoxycytidine + ATP = ADP + dCMP + H(+) 2'-deoxyuridine + ATP = ADP + dUMP + H(+) Monomer. Predominantly expressed in liver, pancreas, muscle, and brain. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the DCK/DGK family.