Chraibi R, Wright M
J Biochem. 1983 Feb;93(2):323-30. doi: 10.1093/oxfordjournals.jbchem.a134184.
Thymidine kinase [ATP: thymidine 5'-phosphotransferase, EC 2.7.1.21] has been purified more than 3,500 fold from microplasmodia of Physarum polycephalum. Properties of the enzyme were determined on preparations purified 1,400 fold. Thymidine was transformed to dTMP while a stoichiometric quantity of ATP was transformed to ADP. 5-Iododeoxyuridine, 5-bromodeoxyuridine, and 5-fluorodeoxyuridine acted as competitive inhibitors for the thymidine substrate while 5-bromodeoxyuridine could be used as a substrate. In contrast uridine did not inhibit the enzymatic activity while deoxyuridine was a very poor competitive inhibitor in agreement with the observation that deoxyuridine could not be used as a substrate. Two apparent Michaelis constants were found for thymidine. Only the highest Michaelis constant could be decreased in the presence of increasing concentrations of ATP. Among the various nucleoside mono, di, or triphosphates studied only ATP and to a less extent dATP could be used as phosphate donors. A non competitive inhibition for thymidine was observed with dTTP. dTMP, dTDP, and dTTP acted as competitive inhibitors for ATP. None of the nucleoside mono, di, or triphosphates studied showed an activatory effect at low concentrations of ATP, even in the presence of dTTP. However, dUTP and dGDP acted as competitive inhibitors for ATP.
胸苷激酶[ATP：胸苷5'-磷酸转移酶，EC 2.7.1.21]已从多头绒泡菌的微质体中纯化了3500多倍。在纯化了1400倍的制剂上测定了该酶的性质。胸苷转化为dTMP，同时化学计量的ATP转化为ADP。5-碘脱氧尿苷、5-溴脱氧尿苷和5-氟脱氧尿苷作为胸苷底物的竞争性抑制剂，而5-溴脱氧尿苷可作为底物。相比之下，尿苷不抑制酶活性，而脱氧尿苷是一种非常弱的竞争性抑制剂，这与脱氧尿苷不能用作底物的观察结果一致。发现胸苷有两个表观米氏常数。只有最高的米氏常数可以在ATP浓度增加时降低。在研究的各种核苷单磷酸、二磷酸或三磷酸中，只有ATP以及程度较小的dATP可作为磷酸供体。观察到dTTP对胸苷有非竞争性抑制作用。dTMP、dTDP和dTTP作为ATP的竞争性抑制剂。即使在存在dTTP的情况下，所研究的核苷单磷酸、二磷酸或三磷酸在低浓度ATP时均未显示出激活作用。然而，dUTP和dGDP作为ATP的竞争性抑制剂。
