title: Absence of pyrimidine salvage and prevention of thymineless radiosensitization in Escherichia coli thyA cells fed dihydrothymine or thymine glycol.
abstract: Little information is available concerning the metabolic fate of radiation-induced thymine base damage products once they have been excised from DNA. The present study was an attempt to determine whether or not thymine-requiring mutants of Escherichia coli could grow on dihydrothymine (DHT) and thymine glycol (TG) by "salvaging" the altered thymines. A second test of thymine product utilization was prevention of thymineless radiosensitization. Results showed that very low growth of Thy- cells on DHT or TG could be explained by the presence of less than or equal to 1% contaminating thymine in the mixtures. Radiation dose-modification factors (DMFs) for thyA cells fed DHT or TG for 3 h were 1.38 +/- 0.28 and 1.26 +/- 0.24, respectively, whereas the DMF for 3 h thymine-starved cells was 1.63 +/- 0.05. The small (approximately 25%) amelioration of thymineless radiosensitization observed in DHT- or TG-fed cells could probably be explained by contaminating thymine in the medium. Although DHT is a normal metabolite in some cells, neither DHT nor TG could be used efficiently by thymine-requiring cells in the protocol presented.
mesh_terms: D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects*; D009154:Mutation; D011743:Pyrimidines / Q000378:metabolism*; D013941:Thymine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*
chemical_list: D011743:Pyrimidines; C029389:thymine glycol; C042836:5,6-dihydrothymine; D013941:Thymine