deoxycytidine, thymidine, or deoxyuridine + ATP => dCMP, TMP, or dUMP + ADP [TK2]

Mitochondrial thymidine kinase 2 (TK2) catalyzes the reactions of deoxycytidine, thymidine, and deoxyuridine with ATP to form the corresponding deoxynucleotide monophosphates and ADP. The enzyme has been purified from human spleen and is active as a monomer (Munch-Petersen et al. 1991). The enzyme requires divalent cations for activity (Mg++ is preferred) but the nature of the association between the metal ion and the enzyme polypeptide is unclear (Lee and Cheng 1976). The mitochondrial localization of the enzyme has been established experimentally for rats and cattle (Jansson et al. 1992); its mitochondrial localization in humans is inferred from these results and the presence of a mitochondrial localization motif at the amino terminus of the open reading frame of a cloned human cDNA that is missing from the mature catalytically active protein (Wang et al. 1999).

线粒体胸苷激酶2（TK2）催化脱氧胞苷、胸苷和脱氧尿苷与三磷酸腺苷（ATP）的反应，生成相应的脱氧核苷单磷酸盐和二磷酸腺苷。此酶已从人类脾脏中纯化，并以单体形式（Munch-Petersen等人，1991年）表现出活性。该酶的活性需要二价阳离子（镁离子（Mg++）更为偏好）作为辅助因子，但其与酶多肽之间的结合性质尚不明确（Lee和Cheng，1976年）。该酶的线粒体定位已在实验上证实于大鼠和牛（Jansson等人，1992年）；人类的线粒体定位则基于这些结果以及克隆的人cDNA开放阅读框氨基末端存在的线粒体定位基序（该基序在成熟的催化活性蛋白中缺失），从而进行推断（Wang等人，1999年）。