Glycogen in Liver: Characteristics and Biosynthesis.

Gannon, Mary C.; Nuttall, Frank Q.; 洋樹, 高田

doi:10.4052/tigg.8.183

Cited by 8 publications

(3 citation statements)

References 3 publications

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“…The number of glycogenin-2 molecules that we estimate to be present in liver is sufficient to allow one per ␣-particle of M r 10 8 and, as noted, we found that essentially all of the glycogenin-2 was attached to carbohydrate. These calculations are not accurate enough to preclude the existence of glycogen molecules free of glycogenin, as discussed by Ercan et al (28,29). Nonetheless, we conclude that there is sufficient glycogenin-2 in liver to have a major impact on glycogen synthesis in that organ.…”

Section: Fig 7 Interaction Of Glycogenin-1 and Glycogenin-2 In Vitromentioning

confidence: 51%

“…Ercan et al (28) had also suggested that in rat liver some glycogen molecules are not attached to protein. This scenario prompted the suggestion (14,29) that glycogenin-1 might be recycled so that each molecule could participate in the synthesis of multiple glycogen molecules. The number of glycogenin-2 molecules that we estimate to be present in liver is sufficient to allow one per ␣-particle of M r 10 8 and, as noted, we found that essentially all of the glycogenin-2 was attached to carbohydrate.…”

Section: Fig 7 Interaction Of Glycogenin-1 and Glycogenin-2 In Vitromentioning

confidence: 99%

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Characterization of Human Glycogenin-2, a Self-glucosylating Initiator of Liver Glycogen Metabolism

Roach

1998

Journal of Biological Chemistry

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Glycogenin-2 is a recently described self-glucosylating protein potentially involved in the initiation of glycogen biosynthesis (Mu, J., Skurat, A. V., and Roach, P. J. (1997) J. Biol. Chem. 272, 27589 -27597). In human liver extracts, most of the glycogenin-2 was only detectable after treatment with ␣-amylase. Similarly, purifed high M r glycogen was only detected after release by ␣-amylase treatment. Based on analysis by polymerase chain reaction, the predominant isoform in liver was glycogenin-2␤. Glycogenin-2 was found in Ewing's sarcoma RD-ES cells where, however, it was not associated with high M r carbohydrate. Both human liver and human RD-ES cell extracts also contained glycogenin-1. Glycogenin-1 and glycogenin-2 interact with one another, based on in vitro interactions and co-immunoprecipitation from liver and cell extracts. Mutation of Tyr-196 in glycogenin-2 to a Phe residue abolished the ability of glycogenin-2 to self-glucosylate but not to interact with glycogenin-1. Stable overexpression of glycogenin-2␣ in Rat-1 fibroblast cells resulted in a 5-fold increase in the level of glycogen present in the low speed pellet but little change in the low speed supernatant. This result is important since it indicates that the level of glycogenin-2 can determine glycogen accumulation and hence has the potential to control glycogen synthesis.

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Section: Fig 7 Interaction Of Glycogenin-1 and Glycogenin-2 In Vitromentioning

confidence: 51%

Section: Fig 7 Interaction Of Glycogenin-1 and Glycogenin-2 In Vitromentioning

confidence: 99%

Characterization of Human Glycogenin-2, a Self-glucosylating Initiator of Liver Glycogen Metabolism

Roach

1998

Journal of Biological Chemistry

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“…It remains then to be elucidated whether this discrepancy in different linebroadening behavior between both physiological conditions can be attributed to differences in the dynamics of biosynthesis of glycogen. 36 The results also demonstrate that S/N is a crucial factor in the performance of the algorithm that has to pick up the changing actual distribution of T 2 -times in glucosyl moieties spatially confined in an expanding glycogen pool. For a single perfused liver in the starved state, where S/N (<13) is low, the fitting model, using a sum of Lorentzian lines, can only fit the glycogen signal with a single Lorentzian for the entire time course.…”

Section: Discussionmentioning

confidence: 92%

Quantification of the glycogen ¹³C‐1 NMR signal during glycogen synthesis in perfused rat liver

et al. 2003

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We studied glycogen synthesis from glucose in perfused livers of fed (n = 4) and 24 h starved (n = 7) rats. Glycogenolysis was inhibited by BAY R3401 (150 microM) and proglycosyn (100 microM). After 60 min, we replaced 99% (13)C-1 glucose by natural abundance glucose. This pulse-chase design allowed us to recognize residual ongoing futile glycogen turnover from the release of initially deposited (13)C-label, into the (13)C-free chase medium. Net residual turnover was less than 2 +/- 0.7% and 0.6 +/- 0.2% of 1-(13)C glycogen deposition rates of 0.31 +/- 0.04 and 0.99 +/- 0.04 micromol glucose g(-1) min(-1), in starved and fed livers, respectively. The 1-(13)C glycogen signal was monitored throughout the experiment with proton-decoupled (13)C NMR spectroscopy and analyzed in the time domain using AMARES. We noticed progressive line-broadening in any single experiment in the chase phase. One or a sum of two to three overlapping Lorentzians, with different exponential damping factors, were fitted to the signal. When the S/N was better than 40, the fit always delivered a small and a broad component. In the chase phase, the fit with a single Lorentzian resulted in a decline of glycogen signal by about 15 +/- 4 and 12 +/- 2% in starved and fed rats, respectively. This apparent decline in 1-(13)C glycogen signal could not be accounted for by the appearance of equivalent amounts of (13)C-labeled metabolites in the perfusate. The fit with a sum of two Lorentzians resulted in a decline of glycogen signal intensity of 7 +/- 5 and 5 +/- 3% in starved and fed rats, respectively, which reduced the apparent turnover to 8 +/- 9% and 6 +/- 4%, respectively. Quantification of the growing (13)C-1 glycogen signal requires a model function that accommodates changes in line shape throughout the period under study.

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Biosynthesis of Glycogen

Roach¹,

Ernst

Hart

et al. 2000

Carbohydrates in Chemistry and Biology

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Glycogen is a branched polymer composed primarily of glucose residues connected via a-1,4-glycosidic and a-1,6-glycosidic linkages. Its biosynthesis requires the participation of three enzymes, glycogenin, glycogen synthase and the glycogen branching enzyme. Glycogen synthase and glycogenin are glucosyl transferases that utilize UDP-glucose as the glucosyl donor. The branching enzyme catalyzes first the hydrolysis of an a-1,4-glycosidic followed by reattachment of the resulting oligosaccharide moiety via an a-1,6-glycosidic linkage, thus creating a branchpoint.Glycogen biosynthesis can be divided into two stages, initiation and bulk polymer synthesis. Initiation is mediated by glycogenin which first catalyzes the attachment of glucose to specific tyrosine residues and thereafter adds further glucose residues, in a-1,4-glycosidic linkages, until the oligosaccharide is 8-20 in length. This "primed" glycogenin then serves as substrate for bulk synthesis by glycogen synthase and branching enzyme to generate mature glycogen. It has been proposed that there is a discrete, intermediate form of glycogen, designated proglycogen, whose concentration is independent of normal mature glycogen. However, the functional significance of proglycogen is controversial and it is not clear that a separate enzymology exists for its controlled metabolism. Glycogen is present in most cell types but, in mammals, is quantitatively highest in skeletal muscle and liver. Many microorganisms also synthesize glycogen and the related compound starch is produced by plants. The polymer is believed to function as a reserve of glucose and its deposition is linked to the nutritional status of the cell or organism. Carbohydrates in Chemistry and Biology

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Glycogen in Liver: Characteristics and Biosynthesis.

Cited by 8 publications

References 3 publications

Characterization of Human Glycogenin-2, a Self-glucosylating Initiator of Liver Glycogen Metabolism

Characterization of Human Glycogenin-2, a Self-glucosylating Initiator of Liver Glycogen Metabolism

Quantification of the glycogen ¹³C‐1 NMR signal during glycogen synthesis in perfused rat liver

Biosynthesis of Glycogen

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Glycogen in Liver: Characteristics and Biosynthesis.

Cited by 8 publications

References 3 publications

Characterization of Human Glycogenin-2, a Self-glucosylating Initiator of Liver Glycogen Metabolism

Characterization of Human Glycogenin-2, a Self-glucosylating Initiator of Liver Glycogen Metabolism

Quantification of the glycogen 13C‐1 NMR signal during glycogen synthesis in perfused rat liver

Biosynthesis of Glycogen

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Quantification of the glycogen ¹³C‐1 NMR signal during glycogen synthesis in perfused rat liver