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Incorporation of Bicarbonate-¹⁴C into Pyrimidines and into Ribonucleic Acid of the Novikoff Ascites Tumor Cell^1,2,

Department of Pharmacology, Baylor University College of Medicine, Houston, Texas 77025

The incorporation of bicarbonate-¹⁴C into pyrimidines of the Novikoff ascites tumor cell has been studied. It was shown that bicarbonate was incorporated into carbamylaspartate and into the C-2 of uracil nucleotides. The incorporation was increased by both glutamine or ammonia; glutamine was the more effective nitrogen donor. Exogenous orotic acid inhibited the formation of uridine monophosphate (UMP) and caused a buildup of labeled carbamylaspartate. The glutamine antagonist, 6-diazo-5-oxo-L-norleucine, inhibited the glutamine-stimulated bicarbonate incorporation into carbamylaspartate.

Bicarbonate-¹⁴C has been shown to be rapidly incorporated into the ribonucleic acid of the Novikoff ascites cell either in vivo or in vitro. The specific activity of the corresponding liver RNA in vivo was approximately to 1/10 that of the Novikoff RNA. Over 50% of the label was present in the UMP portion of the Novikoff RNA and less than 30% was present in the combined purine fraction.

The data suggest that an enzyme is present in the intact Novikoff ascites tumor cell that requires glutamine as the nitrogen donor in the formation of carbamyl phosphate. The incorporation of bicarbonate into UMP is consistent with the operation of the orotic acid pathway in the hepatoma.

¹ This investigation was supported by grants from the USPHS, National Cancer Institute, (CA06571) and National Science Foundation (GB4339) and by an institutional grant from the American Cancer Society (IN-27-G-Project #11).

² Portions of this study have been reported at the American Association for Cancer Research in Denver, Colorado, 1966.

³ Recipient of a Lederle Medical Faculty award.

Received 8/22/66. Accepted 11/ 1/66.