[Purification and some properties of the thymidine kinase from the rat thymus]

Preparation of thymidine kinase, purified 500-fold, was isolated from rat thymus by means of fractionation with ammonium sulphate, gel filtration on Sephadex G-200, treatment with calcium phosphate gel and chromatography on DEAE-cellulose. The enzyme was shown to be stabilized by 0.12 mM of thymidine, activated by Mg2 (optimum concentration 12 mM) and inhibited by Mn2+ATP served as donor of phosphate groups in reactions, catalyzed by thymidine kinase. In respect to the phosphate acceptor the enzyme showed sharp specificity: it used as a substrate only thymidine, deoxyuridine and its derivatives, substituted at the 5-th position by haloid group. In study of affinity of the enzyme for the substrate Km equals 2.5-10 minus 5 M (Vmax equals 0.09) was determined.