Properties of Thymidine Kinase Partially Purified from Human Fetal and Adult Tissue

Properties of thymidine kinase, partially purified from human fetal liver, have been compared with properties of human adult thymidine kinase. Fetal thymidine kinase differs from the adult form in electrophoretic properties, pH optima, heat stability, inhibition by dCTP, and ability to utilize nucleotides other than ATP as phosphate donors. We observe that human fetal thymidine kinase resembles thymidine kinase present in at least two permanent human tumor cell lines and also has properties similar to the enzyme found by other workers in a variety of animal and human tumor cells.