Human liver thymidine kinase. Purification and some properties of the enzyme

Thymidine kinase (EC 2.7.1.21) has been purified 5600-fold to apparent homogeneity from normal adult human liver. The purification included affinity chromatography on a thymidine column. The subunit molecular weight of the enzyme obtained from this purification was 48,000, and human liver thymidine kinase exhibited association and dissociation. The smallest native molecular form had a molecular weight as determined by gel filtration of 49,000 and the enzyme consistently associated into forms with a molecular weight of 98,000 and 340,000. With isoelectric focusing, the enzyme demonstrated a single form with an isoelectric point of 5.1.