Increased activities of thymidine kinase isozymes in human colon polyp and carcinoma

Thymidine kinase (TK), the enzyme in the pyrimidine salvage pathway, and its isozymes were examined in 15 specimens of normal mucosa, 14 polyps and 14 carcinomas in human colon. The average TK activities in colon polyps and carcinomas were about 1.6 and 2.9 times that in normal colon mucosa, respectively. The colon TK isozymes were separated into 2 types by DEAE-cellulose column chromatography. The activity of the TK isozyme eluted with 0.1 M NaCl in buffer was 1.6-fold higher in colon polyp and 1.5-fold higher in colon carcinoma than that in normal colon mucosa. In colon carcinoma, but not colon polyp, the activity of the other isozyme eluted with buffer alone was increased to 5.1-fold that in normal tissues. As the activity of the latter isozyme was not affected by deoxycytidine triphosphate, it may be involved in DNA replication. The results suggest that increases in the activities in the former and latter TK isozymes may indicate tumorigenesis and carcinogenesis, respectively, in the human colon.