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Ribonucleic Acid Nucleotides in Maternal and Fetal Tissues Derive almost Exclusively From Synthesis de novo in Pregnant Mice^1,2,

U.S. Department of Agriculture-Agricultural Research Service, Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX

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 [U¹³C]-purines (0.03–0.2 mol/100 mol) was significantly (P < 0.001) 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 [U¹³C]-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.

KEY WORDS: • mice • nucleic acids • uniformly labeled tracers • purine synthesis • pyrimidine synthesis

¹ This work is a publication of the U.S. Department of Agriculture-Agricultural Research Service, Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine and Texas Children's Hospital, Houston, TX. Funding has been provided from the USDA/ARS under Cooperative Agreement No. 5862501003. The contents of this publication do not necessarily reflect the views or policies of the U.S. Department of Agriculture, nor does mention of trade names, commercial products, or organizations imply endorsement by the United States government.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ Current address: Abbott Laboratories, Camino de Purchil 68, 18004 Granada, Spain.

⁴ To whom correspondence should be addressed.

Manuscript received 12 December 1995. Revision accepted 23 February 1996.

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