title: Regulation by thymidine monophosphate and other nucleotides of thymidine kinase activity in extracts from primary rabbit kidney cells infected by HSV types 1 and 2.
abstract: In an attempt to differentiate between thymidine kinase (EC.2.4.1.21) induced by herpesvirus hominis type I (TK I) and type 2 (TK2), the different susceptibilities to the modifying effects of some thymidine analogues proved to be useful criteria: (I)2'-deoxythymidine-5'-triphosphate (dThd-5'-PPP) inhibits TK 2 at a concentration of 0-125 mM by 90%, whereas TK I is inhibited at 4-03 mM by 50%. (2) 2'-deoxythymidine-5'-monophosphate (dThd-5'-P) competitively inhibits TK 2 at all concentrations tested. On the other hand, the direction of its effect on TK I is concentration dependent: at 500 mum it stimulates and at 8 mM inhibits TK I activity. During enzyme kinetic studies, TK I displays substrate inhibition which is reversed by dThd-5'-P. This result explains the stimulating effect of dThd-5'-P at 500 muM. This phenomenon suggests the existence on the enzyme molecule of a second binding site for dThd which mediates substrate inhibition and which can be occupied also by dThd-5'-P. After polyacrylamide gel electrophoresis of TK I, the stimulation by dThd-5'-P disappears, suggesting the separation of the second binding site from the catalytic centre.
mesh_terms: D002474:Cell-Free System; D046508:Culture Techniques; D007700:Kinetics; D011741:Pyrimidine Nucleosides / Q000494:pharmacology*; D011742:Pyrimidine Nucleotides / Q000494:pharmacology*; D018139:Simplexvirus / Q000201:enzymology*; D013937:Thymidine Kinase / Q000378:metabolism*; D013942:Thymine Nucleotides / Q000494:pharmacology*
chemical_list: D011741:Pyrimidine Nucleosides; D011742:Pyrimidine Nucleotides; D013942:Thymine Nucleotides; D013937:Thymidine Kinase