Determination of Pathways of Glycogen Synthesis and the Dilution of the Three-Carbon Pool with [U-13C]Glucose

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 88; no. 6; pp. 2103 - 2107
• Main Authors: Katz, Joseph, Wals, P. A., W. N. Paul Lee
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 15.03.1991; National Acad Sciences
• Subjects: 550201 - Biochemistry- Tracer Techniques; ALDEHYDES; ANIMALS; BASIC BIOLOGICAL SCIENCES; Biological and medical sciences; BIOLOGICAL PATHWAYS; BIOSYNTHESIS; Blood glucose; BODY; CARBOHYDRATES; Carbon; CARBON 13; CARBON 14 COMPOUNDS; CARBON COMPOUNDS; Carbon cycle; CARBON ISOTOPES; Carbon Radioisotopes; CHROMATOGRAPHY; DIGESTIVE SYSTEM; EVEN-ODD NUCLEI; Fundamental and applied biological sciences. Psychology; GAS CHROMATOGRAPHY; GLANDS; GLUCOSE; Glucose - metabolism; GLYCOGEN; GLYCOLYSIS; HEXOSES; HYDROGEN COMPOUNDS; ISOTOPE APPLICATIONS; Isotope Labeling - methods; ISOTOPES; LABELLED COMPOUNDS; LABELLED POOL TECHNIQUES; LIGHT NUCLEI; LIVER; Liver - metabolism; Liver Glycogen - biosynthesis; MAMMALS; MASS SPECTROSCOPY; Mathematics; METABOLISM; Metabolisms and neurohumoral controls; Models, Biological; Molecules; MONOSACCHARIDES; NUCLEI; ORGANIC COMPOUNDS; ORGANS; Phosphates; POLYSACCHARIDES; Radiocarbon; Radioisotope Dilution Technique; RATS; Recycling; RODENTS; SACCHARIDES; SEPARATION PROCESSES; SPECTROSCOPY; STABLE ISOTOPES; SYNTHESIS; TRACER TECHNIQUES; Trioses; TRITIUM COMPOUNDS; VERTEBRATES; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Radiolabelling; Rat; Glycogen; Rodentia; Glucose; Metabolism; Carbon; Krebs cycle; Gas chromatography; Vertebrata; Dilution; Mammalia; Mass spectrometry; Gluconeogenesis
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.88.6.2103

Rats were infused with glucose at 30 mg/min, containing 18% enriched [U-13C]glucose and [1-14C]- and [3-3H]glucose. The mass isotopomer patterns of13C-labeled blood glucose and liver glycogen were determined by gas chromatography/mass spectroscopy. The contribution of the direct pathway to glycogen was calculated from the three tracers, and the values by all three were nearly identical, about 50%. The14C specific activity in carbon 6 of glycogen glucose was about 6% that of carbon 1. The [3H]glucose/[1-14C]glucose ratio in glycogen was 80-90% that in blood glucose. The enrichment of13C and the specific activity of14C in glycogen formed by the indirect path were 20-25% of glycogen formed directly from glucose. The dilution is of two kinds: (i) an exchange of labeled carbon with unlabeled carbon in the tricarboxylic acid cycle and (ii) dilution by unlabeled nonglucose carbon. Methods to calculate the two types of dilution are presented. In control rats the dilution factor by exchange in the tricarboxylic acid cycle is 1.4, and the dilution by unlabeled carbon is 2.5- to 3.0-fold, with the overall dilution about 4-fold. In rats preinjected with glucagon, the dilution through the tricarboxylic acid cycle was unaffected but that by nonglucose carbon was decreased.