MECHANISMS OF EXCISION OF 5-FLUOROURACIL BY URACIL DNA GLYCOSYLASE INNORMAL HUMAN-CELLS

Recent evidence indicates that 5-fluorouracil (5-FlUra) is incorporate d into DNA and is removed by the DNA repair enzyme uracil DNA glycosyl ase. Synthetic oligonucleotides containing either a single uracil or 5 -FlUra residue were constructed to examine the mechanisms by which hum an cells remove 5-FlUra from DNA. The human uracil DNA glycosylase exc ised uracil in a manner similar to that observed for the bacterial enz yme. In contrast, a significant difference was observed in their abili ties to remove 5-FlUra. In particular, both the bacterial an normal hu man enzymes displayed 13-17-fold increases in their apparent K(m) valu es but the apparent V(max) values remained virtually constant. These r esults demonstrate that normal human cells possess a defined capacity to remove 5-FlUra incorporated into DNA. However, specific kinetic dif ferences may exist that affect their capacity to remove 5-FlUra formed in DNA after treatment with this cancer chemotherapeutic agent.