Increased activity of thymidine kinase isozyme in human colon tumor

Thymidine kinase (TK), the salvage pathway enzyme, and its isozymes were examined in normal mucosa and carcinoma of the colon in 13 patients. In colon tumor TK activity increased to 328% of activity of normal colon. The colon TK isozymes were separated from the normal mucosa and carcinoma by DEAE-cellulose column chromatography. The TK isozyme eluted from the column by the elution buffer alone without NaCl was markedly higher (12-fold) in activity in carcinoma than in normal mucosa of the colon and is not affected by dCTP. The TK isozyme unaffected by dCTP has also been reported to be clearly involved in DNA synthesis. This isozyme, whose molecular weight is 100 000 by means of high performance liquid chromatography, is thought to be involved in DNA replication. The results indicate the applicability of the molecular correlation concept to carcinogenesis of colon.