| Popis: |
The contributions of dietary nucleotides and nucleotides synthesized de novo to ribonucleic acid synthesis in vivo were estimated by feeding, from d 13 to 18 of gestation, two groups of five pregnant mice a defined diet that contained either uniformly [U13C]-labeled nucleotides or [U13C]-algal amino acids isolated from algal biomass. Ribonucleic acid and protein were isolated from mucosa, liver and fetus. Nucleosides and amino acids were isolated and converted to their trimethylsilyl and n-propyl ester, heptaflurobutyramide derivatives, respectively. The isotopic enrichments of all isotopomers were determined by gas chromatography-mass spectrometry. In the mice that ingested [U13C]-nucleotides, the isotopic enrichment of [Ul3C]-purines (0.03-0.2 mol/100 mol) was significantly (P0.001) less than that of [U13C]-uridine (1.5-4.2 mol/100 mol). [13C5]-Purines (0.1-0.8 mol/100 mol) and [13C4]-uridine (0.2-0.5 mol/100 mol) were detected, showing that some dietary bases and ribose were incorporated via the salvage pathway. In mice that Ingested U13C-amino acids, the isotopic enrichment (2-4.6 mol/100 mol) of the [13C2]-purines, which derive from [Ul3C]-glycine, was between 73 (liver) and 113% (fetus) of protein-bound 13C2-glycine. The isotopic enrichment (0.8-1.6 mol/100 mol) of [13C3]-uridine, an isotopomer that derives from [U13C]-aspartate, was 50 (liver) to 126% (mucosa) of [13C4]-protein-bound aspartate. The results suggest that a large majority of the bases incorporated into maternal and fetal ribonucleic acids derive from synthesis de novo. |
