Action Patterns of Phosphorylase and Glycogen Synthetase on Glycogen

Parodi, Armando J.; Mordoh, José; Krisman, Clara R.; Leloir, Luis F.

doi:10.1111/j.1432-1033.1970.tb01109.x

Cited by 16 publications

(11 citation statements)

References 27 publications

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“…No close comparison can be made between this distribution and others (e.g. Parodi, 1967;Parodi et al, 1970) obtained with the method described by Mordoh et al (1966) because of the crudeness of calibration of the latter method. However, it is clear that these authors are assigning much higher molecular weights in comparison with the sedimentation coefficients which they calculated.…”

Section: Resultsmentioning

confidence: 58%

The molecular size and shape of liver glycogen

Geddes¹,

Harvey²,

Wills³

1977

Biochemical Journal

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The molecular-weight distribution of liver glycogen has been established from the analysis of sedimentation rates of fractions separated on sucrose density gradients and from the direct measurement of the diffusion coefficients of these fractions by laser-intensity-fluctuation spectroscopy. Hydrodynamic studies indicated that all fractions of glycogen of mol.wt.exceeding 25x10(6) had about 1.1 g of water per g of polysaccharide associated with them. The hydration and hydrodynamic behaviour of all fractions of mol.wt. exceeding 25x10(6) was similar, whereas smaller fractions behaved anomalously, indicating a substantially different overall structure.

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Section: Resultsmentioning

confidence: 58%

The molecular size and shape of liver glycogen

Geddes¹,

Harvey²,

Wills³

1977

Biochemical Journal

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“…In studies on high molecular weight glycogen we detected some labile bonds, the rupture of which decreased the molecular weight from 3000 million to 8 million [15]. Perhaps those labile bonds correspond to the acid-labile glucan-protein bond described.…”

Section: Discussionmentioning

confidence: 99%

A Precursor of Glycogen Biosynthesis: α‐1,4‐Glucan‐Protein

Krisman

Barengo

1975

European Journal of Biochemistry

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128

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The mechanism of glycogen biosynthesis in the absence of added primers takes place at least in two different steps. The first step could be initiated by a new enzyme named glycogen intiator synthase that catalyzes the transfer of glucose from UDP-glucose to an acceptor protein. This step takes place in vitro only in the presence of some salts at high concentration. The complex product from this reaction has been isolated and demonstrated to act as a precursor for the synthesis of glycogen which takes place in the second step and is catalyzed by the already known glycogen synthase.Since glycogen synthase was discovered by Leloir and Cardini [l] a great deal of research has been done on the biosynthesis of glycogen but very little is known about the mechanism by which the molecules start to grow. It is generally accepted that glycogen synthases function only in the presence of primers that can be glycogen or oligosaccharides [2-41. On the other hand, we have recently shown that glycogen synthetase isolated from rat liver catalyzes the transfer of labelled glucose from UDP-[U-'4C]glucose to protein or protein-bound oligosaccharides when no primer is added [5,6]. The product formed is completely solubilized by treatment with pronase or amylase. It is also alkali-stable but acid-labile and contains a-1 ,Clinked glucosyl residues.In this paper we present results that demonstrate that the initial acceptor for the synthesis of glycogen is therefore a protein. MATERIALS AND METHODS UDP-glucose was obtained from Sigma ChemicalCompany. UDP-[U-'4C]-glucose was prepared according to the method of Wright and Robbins [7].The rat liver enzyme preparation and the determination of enzyme activity was carried out as described in previous papers [5,6].Liver branching enzyme was purified as described previously [8] but the livers were thoroughly perfused Enzymes. Glycogen synthase (EC 2.4.1.11) ; 1 ,Ca-glucan branching enzyme (EC 2.4.1.18).with 250mM sucrose, 5mM EDTA and 10mM mercaptoethanol.Paper chromatography of oligosaccharides was performed with butanol-pyridine -water (4 : 3 : 4)as solvent [9]. Sugar and polyalcohol standard spots were developed with the silver nitrate reagent [lo]. Glycogen was estimated by the iodine-CaC1, method [ll]. Borohydride Reduction and Total Hydrolysis of Glycogen PrecursorTo 1 pmol oligosaccharides 17 pmol sodium borohydride was added in 0.3 ml water. After 20 h at room temperature, the reaction was terminated by the addition of 100 pl 5 N HC1, and boric acid was removed by repeated addition of methanol and evaporation.

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“…It has also been suggested that GS is able to add several glucosyl residues successively to the same chain of a glycogen molecule, i.e. that elongation is processive . However, such a pattern of elongation is incompatible with a rapid equilibrium random mechanism, which predicts that exactly one glucose residue is successively incorporated in the same chain (distributive elongation) .…”

Section: Glycogen Synthase and Its Kineticsmentioning

confidence: 99%

Regulation of glycogen synthase from mammalian skeletal muscle – a unifying view of allosteric and covalent regulation

2012

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It is widely accepted that insufficient insulin-stimulated activation of muscle glycogen synthesis is one of the major components of non-insulindependent (type 2) diabetes mellitus. Glycogen synthase, a key enzyme in muscle glycogen synthesis, is extensively regulated, both allosterically (by glucose-6-phosphate, ATP, and others) and covalently (by phosphorylation). Although glycogen synthase has been a topic of intense study for more than 50 years, its kinetic characterization has been confounded by its large number of phosphorylation states. Questions remain regarding the function of glycogen synthase regulation and the relative importance of allosteric and covalent modification in fulfilling this function. In this review, we consider both earlier kinetic studies and more recent site-directed mutagenesis and crystal structure studies in a detailed qualitative discussion of the effects of regulation on the kinetics of glycogen synthase. We propose that both allosteric and covalent modification of glycogen synthase may be described by a Monod-Wyman-Changeux model in terms of apparent changes to L, the equilibrium constant for transition between the T and R conformers. As, with the exception of L, all parameters of this model are independent of the glycogen synthase phosphorylation state, the need to determine kinetic parameters for all possible states is eliminated; only the relationship between a particular state and L must be established. We conclude by suggesting that renewed efforts to characterize the relationship between phosphorylation and the kinetics of glycogen synthase are essential in order to obtain a better quantitative understanding of the function of glycogen synthesis regulation. The model we propose may prove useful in this regard.Abbreviations ADP-Glc, ADP-glucose; AMPK, AMP-activated protein kinase; AtGS, Agrobacterium tumefaciens glycogen synthase; CaMKII, calmodulindependent protein kinase II; CK1, casein kinase 1; CK2, casein kinase 2; D form, glucose-6-phosphate-dependent form of glycogen synthase; DYRK, dual-specificity tyrosine-phosphorylated and tyrosine-regulated protein kinase; EcGS, Escherichia coli glycogen synthase; G6P, glucose-6-phosphate; GP, glycogen phosphorylase; GS, glycogen synthase; GSK3, glycogen synthase kinase 3; I form, glucose-6-phosphate-independent form of glycogen synthase; MWC, Monod-Wyman-Changeux; p38MAPK, mitogen-activated protein kinase; PaGS, Pyrococcus abyssi glycogen synthase; PASK, Per/Arnt/Sim domain-containing protein kinase; PhK, phosphorylase kinase; PKA, cAMPdependent protein kinase; PP1, protein phosphatase 1; PP2A, protein phosphatase 2A; ScGS, Saccharomyces cerevisiae glycogen synthase; UDP-Glc, uridine diphosphate glucose.

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Action Patterns of Phosphorylase and Glycogen Synthetase on Glycogen

Cited by 16 publications

References 27 publications

The molecular size and shape of liver glycogen

The molecular size and shape of liver glycogen

A Precursor of Glycogen Biosynthesis: α‐1,4‐Glucan‐Protein

Regulation of glycogen synthase from mammalian skeletal muscle – a unifying view of allosteric and covalent regulation

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