Abstract
Thymidine kinase (EC 2.7.1.21) from regenerating rat liver has been purified 70 000-fold to apparent homogeneity by affinity chromatography. Molecular weight of the native enzyme was found to be about 54 000, as determined by gel filtration. Electrophoresis in polyacrylamide gels containing sodium dodecyl sulfate yielded a single band with a molecular weight of 26 000, suggesting that thymidine kinase is a dimer of very similar or identical subunits. The Michaelis constant for thymidine is 2.2 μM. ATP acts as a sigmoidal substrate with a ‘ K m’ of 0.2 mM. Reaction kinetics and product inhibition studies reveal the enzymatic mechanism to be sequential.
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