Incorporation of bicarbonate-14 C into pyrimidines and into ribonucleic acid of the Novikoff ascites tumor cell.

The incorporation of bicarbonate-14C into pyrimidines of the Xovikoff aceites 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 undine monophosphate (UMP) and caused a buildup of labeled earbamylaspartate. The glutamine antagonist, 6-diazo-5-oxo-Lnorleucine, inhibited the glutamine-sti mula ted bicarbonate in corporation into carbamylaspartate. Bicarbonate-I4C has been shown to be rapidly incorporated into the ribonucleic acid of the Xovikoff aseites cell either in vivo or in vitro. The specific activity of the corresponding liver RXA in vivo was approximately ìto iV that of the Xovikoff RXA. Over 50% of the label was present in the UMP portion of the Xovikoff RXA and less than 30% was present in the combined purine fraction. The data suggest that an enzyme is present in the intact Novikoff aseites tumor cell that requires glutamine as the nitro gen donor in the formation of carbamyl phosphate. The incorpor ation of bicarbonate into I'MP is consistent with the operation