title: Apparent synergism between amino donors for CTP synthesis in Chinese hamster fibroblasts.
abstract: The synergistic effects of potential amino donors were studied in the assay of CTP synthetase in extracts of Chinese hamster fibroblasts. We found that L-glutamine was not effective as the sole amino donor, but combinations of L-glutamine with NH4HCO3, L-arginine or potassium phosphate did result in the conversion of UTP to CTP. L-arginine or potassium phosphate were also not effective when used alone, and NH4HCO3 was only slightly effective. Our studies demonstrate that the individual synergistic combinations were not additive; multiple combinations of components decreased rather than increased the formation of CTP. The synergistic combinations of L-glutamine with either NH4HCO3 or L-arginine had an absolute requirement for ATP; when ATP and PEP were absent no conversion of UTP to CTP occurred. The presence of GTP in a reaction mixture slightly increased the formation of CTP when L-glutamine and NH4HCO3 were used and substantially increased CTP formation when L-glutamine and L-arginine were used. De novo CTP synthesis was greatly reduced when nonradioactive CTP was added to an assay mixture, suggesting feedback inhibition. A TLC procedure has been developed that allows for the direct separation of UTP and CTP without requiring prior conversion to the mononucleotide or nucleoside level.
mesh_terms: D000818:Animals; D001120:Arginine / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism*; D019731:Carbon-Nitrogen Ligases; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D003570:Cytidine Triphosphate / Q000096:biosynthesis*; D003597:Cytosine Nucleotides / Q000096:biosynthesis*; D004357:Drug Synergism; D005973:Glutamine / Q000378:metabolism*; D008025:Ligases / Q000378:metabolism*; D008168:Lung; D014544:Uridine Triphosphate / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D003597:Cytosine Nucleotides; D005973:Glutamine; C027043:ammonium bicarbonate; D003570:Cytidine Triphosphate; D001120:Arginine; D008025:Ligases; D019731:Carbon-Nitrogen Ligases; C019951:CTP synthetase; D014544:Uridine Triphosphate