The comparative utilization of uracil-2-C14 by liver, intestinal mucosa, and Flexner-Jobling carcinoma in the rat.

Summary 1.When uracil-2-C 14 was administered to tumor-bearing rats, it was utilized for acid-soluble nucleotide formation and RNA and DNA nucleic acid pyrimidine biosynthesis to a much greater extent by the Flexner-Jobling carcinoma and intestinal mucosa than by liver. 2.In a direct comparison of the utilization of uracil-2-C 14 and orotic acid-4-C 14 in vivo , the latter was incorporated into acid-soluble and nucleic acid pyrimidines to a much greater extent in the liver. In intestinal mucosa orotic acid was more efficiently utilized than uracil, while in the tumor the two precursors were incorporated to the same extent. 3.In the soluble, high-speed supernatant fraction obtained from homogenates of liver and Flexner-Jobling carcinoma, there was an extensive conversion of orotic acid into the acid-soluble uridine nucleotides and a much lesser utilization of uracil. There was a somewhat higher conversion of dihydrouracil into nucleotides than of uracil. Extensive catabolism of both uracil and dihydrouracil was observed in this system derived from liver; very little was obtained in the tumor system.