Thymidine Kinase 1, Soluble (TK1)

Thymidine kinase (EC 2.7.1.21) catalyzes the phosphorylation of thymidine to deoxythymidine monophosphate. Genetic variation in soluble thymidine kinase has not been identified in man. Weiss and Green (1967) found that fusion of mouse cells lacking this enzyme with normal human cells could be achieved, that progressive loss of human chromosomes from the hybrid occurred with passage of time, and that at a stage when only one human chromosome remained the cell still had the capacity to synthesize thymidine kinase. Two forms of Thymidine kinase 1, soluble have been identified in animal cells, one in cytosol and one in mitochondria. Activity of the cytosolic enzyme is high in proliferating cells and peaks during the S-phase of the cell cycle; it is very low in resting cells.