Thymidine kinase isoenzymes in human acute and chronic lymphatic leukemia.

The dominating thymidine kinase isoenzyme was examined in mononuclear leucocytes from two patients, one with acute and one with chronic lymphatic leukemia. The two isoenzymes exhibited Michaelis-Menten substrate kinetics with ATP and cooperative inhibition kinetics with dTTP. The substrate kinetics with thymidine were different. According to the enzymatic properties the isoenzymes from the acute and chronic lymphatic cells were designated TK 3 and TK 4, respectively. Comparison with the isoenzymes in normal lymphocytes (TK 1, TK 2) and in acute monocytic leukemic cells (TK 3, TK 4) indicated the existence of three thymidine kinase isoenzymes in human leukemic cells which differed from the two isoenzymes in normal human lymphocytes.