Glucose phosphorylation is not rate limiting for accumulation of glycogen from glucose in perfused livers from fasted rats
Incorporation of Glc and Fru into glycogen was measured in perfused livers from 24-h fasted rats using (6-3H)Glc and (U-14C)Fru. For the initial 20 min, livers were perfused with low Glc (2 mM) to deplete hepatic glycogen and were perfused for the following 30 min with various combinations of Glc and Fru. With constant Fru (2 mM), increasing perfusate Glc increased the relative contribution of Glc carbons to glycogen (7.2 +/- 0.4, 34.9 +/- 2.8, and 59.1 +/- 2.7% at 2, 10, and 20 mM Glc, respectively; n = 5 for each). During perfusion with substrate levels seen during refeeding (10 mM Glc, 1.8 mumol/g/min gluconeogenic flux from 2 mM Fru), Fru provided 54.7 +/- 2.7% of the carbons for glycogen, while Glc provided only 34.9 +/- 2.8%, consistent with in vivo estimations. However, the estimated rate of Glc phosphorylation was at least 1.10 +/- 0.11 mumol/g/min, which exceeded by at least 4-fold the glycogen accumulation rate (0.28 +/- 0.04 mumol of glucose/g/min). The total rate of glucose 6-phosphate supply via Glc phosphorylation and gluconeogenesis (2.9 mumol/g/min) exceeded reported in vivo rates of glycogen accumulation during refeeding. Thus, in perfused livers of 24-h fasted rats there is an apparent redundancy in glucose 6-phosphate supply. These results suggest that the rate-limiting step for hepatic glycogen accumulation during refeeding is located between glucose 6-phosphate and glycogen, rather than at the step of Glc phosphorylation or in the gluconeogenic pathway.
- Research Organization:
- Univ. of Southern California Medical School, Los Angeles (USA)
- OSTI ID:
- 6397237
- Journal Information:
- J. Biol. Chem.; (United States), Journal Name: J. Biol. Chem.; (United States) Vol. 264:1; ISSN JBCHA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
ALDEHYDES
ANIMALS
BIOLOGICAL ACCUMULATION
BIOLOGICAL PATHWAYS
BODY
CARBOHYDRATES
CARBON 14 COMPOUNDS
CHEMICAL REACTIONS
DIGESTIVE SYSTEM
FASTING
FRUCTOSE
GLANDS
GLUCOSE
GLYCOGEN
HEXOSES
ISOTOPE APPLICATIONS
ISOTOPE DILUTION
KETONES
LABELLED COMPOUNDS
LIVER
MAMMALS
MONOSACCHARIDES
ORGANIC COMPOUNDS
ORGANS
PERFUSED ORGANS
PHOSPHORYLATION
POLYSACCHARIDES
RATS
RODENTS
SACCHARIDES
TRACER TECHNIQUES
TRITIUM COMPOUNDS
VERTEBRATES