title: X-irradiation effects on thymidine kinase (TK): II. The significance of deoxythymidine triphosphate for inhibition of TK1 activity.
abstract: The purpose of this study was to investigate the mechanism behind the high sensitivity of thymidine kinase 1 (TK1) to X-irradiation. The deoxythymidine triphosphate (dTTP) pool was studied in mouse ascites tumour cells 1-24 h after X-irradiation with 5 Gy. Irradiation changed the Michaelis-Menten kinetics of TK1 from linear to biphasic, showing a negative co-operativity. These changes were closely related to changes in the dTTP pool. Addition of dTTP to the cell extract of non-irradiated cells, or thymidine (dTdR) to the culture medium, resulted in changes very similar to the kinetics found in the irradiated cells. Addition of 5 cent-amino-5 cent-deoxythymidine (5 cent-AdTdR), a thymidine analogue that eliminated the inhibitory effect of dTTP on TK1 activity, completely abolished the irradiation-induced inhibition of TK1 activity. We suggest that the reduced TK1 activity is mainly due to an elevated intracellular concentration of dTTP.
authors.affiliation: Department of Oncology, KFC, Huddinge University Hospital AB, S-141 86, Stockholm, Sweden. Qimin.He@onkpat.ki.se
authors.forename: Q
authors.initials: Q
authors.lastname: He
authors.forename: S
authors.initials: S
authors.lastname: Skog
authors.forename: I
authors.initials: I
authors.lastname: Welander
authors.forename: B
authors.initials: B
authors.lastname: Tribukait
mesh_terms: D000818:Animals; D002286:Carcinoma, Ehrlich Tumor; D015224:Dideoxynucleosides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D005260:Female; D051379:Mice; D008815:Mice, Inbred Strains; D017693:Sodium Bicarbonate / Q000494:pharmacology; D013379:Substrate Specificity; D013937:Thymidine Kinase / Q000378:metabolism* / Q000528:radiation effects*; D013942:Thymine Nucleotides / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000201:enzymology / Q000528:radiation effects; D014965:X-Rays
chemical_list: D015224:Dideoxynucleosides; D013942:Thymine Nucleotides; C024082:5'-amino-5'-deoxythymidine; D017693:Sodium Bicarbonate; D013937:Thymidine Kinase; C092717:thymidine kinase 1; C024157:thymidine 5'-triphosphate