[Thymidine kinase and its isozyme activities in human thyroid diseases]

An increase in DNA synthesis runs parallel with an increase in the activity of cytoplasmic thymidine kinase (TK), an enzyme that catalyses the phosphorylation of deoxythymidine via the pyrimidine salvage pathway. In this work, I measured TK and its isozyme activities in normal thyroid tissue, Basedow's disease, adenomatous goiter, adenoma and adenocarcinoma of human thyroid glands. TK activity was assayed by the method of Taylor et al. The average TK activities in Basedow's disease, adenomatous goiter, adenoma and adenocarcinoma were 1.78, 1.75, 2.98 and 3.33 times than that in normal thyroid tissue, respectively. TK isozymes were separated by DEAE cellulose (DE-52, Whatman, Kent, UK) column chromatography (1.5 X 5.0 cm). The activities eluted at NaCl concentrations of 0M, 0.1M and 0. 2 M were named peak A,B and C, respectively. The average activities in peaks A and C were not significantly different from each other in these diseases. But the average activity of peak B in the thyroid adenocarcinoma was significantly higher (2.3 fold) than that in normal thyroid tissue. As the activity of this isozyme was not affected by deoxycytidine triphosphate (dCTP), it may be involved in DNA replication closely.