Partial Purification of a Thymidine Phosphorylase from Human Gastric Cancer

A thymidine phosphorylase (TP) preparation was partially purified from human gastric cancer (poorly differentiated adenocarcinoma). The specific activity of the final preparation represented a 379-fold purification of the 7000g supernatant of tissue homogenate. The phosphorolytic activities toward thymidine (dThd), 5’-deoxy-5-fluorouridine (5’-DFUR), and l-(tetrahydro-2-furanyl)-5-fluorouracil (Tegafur) remained closely in parallel during the whole purification procedure. The results provide evidence in support of the assumption that 5’-DFUR and Tegafur are converted into 5-fiuorouracil, an activated form of the antitumor agents, in human tumor tissues by a TP activity. The values of K_mof the TP preparation were 1.68 x 10~₄, 1.72 x 10_–3, 1.33 x 10_–2, and 4.76 x 10-2 m for dThd, 5’-DFUR, Tegafur, and uridine, respectively.