title: Glutamine: precursor or nitrogen donor for citrulline synthesis?
abstract: Although glutamine is considered the main precursor for citrulline synthesis, the current literature does not differentiate between the contribution of glutamine carbon skeleton vs. nonspecific nitrogen (i.e., ammonia) and carbon derived from glutamine oxidation. To elucidate the role of glutamine and nonspecific nitrogen in the synthesis of citrulline, l-[2-(15)N]- and l-[5-(15)N]glutamine and (15)N-ammonium acetate were infused intragastrically in mice. The amino group of glutamine labeled the three nitrogen groups of citrulline almost equally. The amido group and ammonium acetate labeled the ureido and amino groups of citrulline, but not the delta-nitrogen. D(5)-glutamine also infused in this arm of the study, which traces the carbon skeleton of glutamine, was utilized poorly, accounting for only 0.2-0.4% of the circulating citrulline. Dietary glutamine nitrogen (both N groups) incorporation was 25-fold higher than the incorporation of its carbon skeleton into citrulline. To investigate the relative contributions of the carbon skeleton and nonspecific carbon of glutamine, arginine, and proline to citrulline synthesis, U-(13)C(n) tracers of these amino acids were infused intragastrically. Dietary arginine was the main precursor for citrulline synthesis, accounting for approximately 40% of the circulating citrulline. Proline contribution was minor (3.4%), and glutamine was negligible (0.4%). However, the glutamine tracer resulted in a higher enrichment in the ureido group, indicating incorporation of nonspecific carbon from glutamine oxidation into carbamylphosphate used for citrulline synthesis. In conclusion, dietary glutamine is a poor carbon skeleton precursor for the synthesis of citrulline, although it contributes both nonspecific nitrogen and carbon to citrulline synthesis.
authors.affiliation: Children's Nutrition Research Center, Department of Pediatrics, United States Department of Agriculture/Agricultural Research Service, 1100 Bates Street, Houston, TX 77030, USA. marini@bcm.edu
authors.forename: Juan C
authors.initials: JC
authors.lastname: Marini
authors.forename: Inka Cajo
authors.initials: IC
authors.lastname: Didelija
authors.forename: Leticia
authors.initials: L
authors.lastname: Castillo
authors.forename: Brendan
authors.initials: B
authors.lastname: Lee
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001120:Arginine / Q000097:blood / Q000378:metabolism*; D002247:Carbon Isotopes / Q000097:blood / Q000494:pharmacology; D002956:Citrulline / Q000096:biosynthesis* / Q000097:blood; D041981:Gastrointestinal Tract / Q000378:metabolism*; D005973:Glutamine / Q000097:blood / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D051379:Mice; D008813:Mice, Inbred ICR; D009584:Nitrogen / Q000378:metabolism; D009587:Nitrogen Isotopes / Q000097:blood / Q000494:pharmacology; D011392:Proline / Q000097:blood / Q000378:metabolism*; D011897:Random Allocation; D013047:Specific Pathogen-Free Organisms
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D005973:Glutamine; D002956:Citrulline; D000641:Ammonia; D001120:Arginine; D011392:Proline; D009584:Nitrogen
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