Human thymidine kinase: purification and some properties of the TK1 isoenzyme from placenta

Human thymidine kinase TK1 isoenzyme has been purified 1800-fold from placenta to a specific activity of 2.9 nmoles/min/mg of protein. The rapid purification procedure includes affinity chromatography on a thymidine-Sepharose column. At all stages of purification, the enzyme showed irreversible lability. The native molecular weight was determined to be 45000. Human placental TK1 exhibited specificity for ATP and thymidine as substrates, and significant inhibition was found only with thymidine nucleotides. TTP was the most effective inhibitor.