Thymidylate synthetase activity in the Novikoff hepatoma.
The mechanism by which injected methotrexate increases thymidylate synthetase activity in the Novikoff hepatoma has been studied. Folic acid injection causes a similar increase in enzyme activity in hepatoma after 16 hr but the action of folic acid and methotrexate is not additive. The increase in activity of thymidine 5'-phosphate synthetase in the hepatoma caused by methotrexate is not affected by actinomycin D, but is inhibited 50% by puromycin and 100% by cycloheximide. High-speed supernatent fraction prepared from hepatoma of animals treated with methotrexate has, initially, one-half the specific thymidine 5'-phosphate synthetase activity of untreated controls. Upon addition of increasing amounts of tetrahydrofolate, the specific enzyme activity in the supernatant fraction from the methotrexate-treated animals rises to double that of the controls. Puromycin added to homogenates of Novikoff hepatoma consistently increases enzyme activity by approximately 20%. One hypothesis consistent with these results and results reported by others is presented.
D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D005492:Folic Acid / Q000494:pharmacology; D008113:Liver Neoplasms / Q000201:enzymology*; D008297:Male; D008727:Methotrexate / Q000494:pharmacology; D008780:Methyltransferases / Q000378:metabolism*; D009374:Neoplasms, Experimental / Q000201:enzymology; D011691:Puromycin / Q000494:pharmacology; D051381:Rats; D013763:Tetrahydrofolates / Q000494:pharmacology; D013940:Thymidylate Synthase / Q000032:analysis / Q000378:metabolism*
D013763:Tetrahydrofolates; D003609:Dactinomycin; D011691:Puromycin; D005492:Folic Acid; D003513:Cycloheximide; D008780:Methyltransferases; D013940:Thymidylate Synthase; D008727:Methotrexate