Detection of thymidine kinase activity using an assay based on the precipitation of nucleoside monophosphates with lanthanum chloride

A new assay method for the measurement of thymidine kinase (TK) is described. Cytosols were prepared from TK − and TK + cells and evaluated for TK activity using an assay which is based on the phosphorylation of [ 125 I]-iododeoxyuridine, [ 125 I]-iododeoxycytidine, or [ 3 H]thymidine and the precipitation of the monophosphates of these nucleosides by lanthanum chloride. The specificity, reproducibility, sensitivity, and convenience of this assay are demonstrated.