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At least 307 records · Page 17Linked to original sources
PubMed1986

The initiation of glycogen biosynthesis in rat heart alpha-1,4 glucans tightly associated with glycogen synthase.

A partially purified glycogen synthase from rat cardiac muscle transferred glucosyl residues from UDP-[14C]glucose to an endogenous protein acceptor in the absence of added primer. After native gel electrophoresis of the enzyme preparation, unprimed activity was detected. Primer-dependent and independent activities were found in the same position. After denaturing gel electrophoresis of the reaction products, radioactivity comigrated with protein. Pulse-chase experiments showed that the size of the reaction products increased as a function of time. These products were degraded by amyloglucosidase, thus suggesting that glycogen-like molecules had grown on the protein acceptor. The activity of the enzyme was markedly reduced upon preincubation with alpha-amylase. Therefore, preformed protein-bound alpha-1,4-glucans were acting as primers. The glucoprotein acceptor may be a protein strongly associated with glycogen synthase, or alternatively, the enzyme itself.

Animals↗
PubMed1977

Biosynthesis of bacterial glycogen: genetic and allosteric regulation of glycogen biosynthesis in Salmonella typhimurium LT-2.

Structural gene mutants of the glycogen biosynthetic enzymes adenosine diphosphate glucose pyrophosphorylase (glgC) and glycogen synthase (glgA) were isolated and partially characterized. The cotransduction frequencies of these genes with the aspartic semialdehyde dehydrogenase (asd) and glycerol-3-phosphate dehydrogenase (glpD) genes suggested the unambiguous gene order of glpD glgA glgC asd. The results of the three-factor cross glpD- glgA- glgC+ X glpD+ glgA+ glgC- were consistent with the proposed order. A simultaneous and approximately equivalent derepression of the glgC, glgA, and glgB (branching enzyme) gene products was observed in the late logarithmic-early stationary phase of growth on enriched media. These results are consistent with the coordinately regulated synthesis of the three glycogen biosynthetic enzymes in Salmonella typhimurium.

Genes↗
PubMed2001

Physiological hyperinsulinemia impairs insulin-stimulated glycogen synthase activity and glycogen synthesis.

Although chronic hyperinsulinemia has been shown to induce insulin resistance, the basic cellular mechanisms responsible for this phenomenon are unknown. The present study was performed 1) to determine the time-related effect of physiological hyperinsulinemia on glycogen synthase (GS) activity, hexokinase II (HKII) activity and mRNA content, and GLUT-4 protein in muscle from healthy subjects, and 2) to relate hyperinsulinemia-induced alterations in these parameters to changes in glucose metabolism in vivo. Twenty healthy subjects had a 240-min euglycemic insulin clamp study with muscle biopsies and then received a low-dose insulin infusion for 24 (n = 6) or 72 h (n = 14) (plasma insulin concentration = 121 +/- 9 or 143 +/- 25 pmol/l, respectively). During the baseline insulin clamp, GS fractional velocity (0.075 +/- 0.008 to 0.229 +/- 0.02, P < 0.01), HKII mRNA content (0.179 +/- 0.034 to 0.354 +/- 0.087, P < 0.05), and HKII activity (2.41 +/- 0.63 to 3.35 +/- 0.54 pmol x min(-1) x ng(-1), P < 0.05), as well as whole body glucose disposal and nonoxidative glucose disposal, increased. During the insulin clamp performed after 24 and 72 h of sustained physiological hyperinsulinemia, the ability of insulin to increase muscle GS fractional velocity, total body glucose disposal, and nonoxidative glucose disposal was impaired (all P < 0.01), whereas the effect of insulin on muscle HKII mRNA, HKII activity, GLUT-4 protein content, and whole body rates of glucose oxidation and glycolysis remained unchanged. Muscle glycogen concentration did not change [116 +/- 28 vs. 126 +/- 29 micromol/kg muscle, P = nonsignificant (NS)] and was not correlated with the change in nonoxidative glucose disposal (r = 0.074, P = NS). In summary, modest chronic hyperinsulinemia may contribute directly (independent of change in muscle glycogen concentration) to the development of insulin resistance by its impact on the GS pathway.

Adult↗
PubMed1991

Glycogen and enzymes of glycogen metabolism in rat embryos and fetal organs.

Glycogen content and the enzymes of glycogen metabolism have been measured in the postimplantation rat embryo over a period ranging from 9.5 to 18.5 days of gestation. The earliest periods studied were at days 9.5 and 10.5 of gestation, when the yolk sac becomes vascularized and heart beat is first established. The next intervals were at days 10.5-11.5 when vascular connections via the allantoic placenta are formed. At 14.5 and 18.5 days of development, 4 entire organs were analyzed; heart, liver, kidney and brain. The metabolic apparatus of glycogen metabolism was concentrated in the embryo at 10.5 days, then the heart region, and in the heart itself at later stages.

Animals↗
PubMed2006

Purification of glycogen debranching enzyme from porcine brain: evidence for glycogen catabolism in the brain.

Amylo-1,6-glucosidase from porcine brain was purified to homogeneity by ammonium sulfate fractionation, followed by sequential steps of liquid chromatography on DEAE-Sephacel, Sephacryl S-300, and Super Q. The purified enzyme had both maltooligosaccharide transferase and amylo-1,6-glucosidase activities within a single polypeptide chain, and the combination of these two activities removed the branches of phosphorylase limit dextrin. Based on these results, the purified enzyme was identified as a glycogen debranching enzyme (GDE). The molecular weight of the brain GDE was 170,000 by gel-filtration and 165,000 by reducing SDS-PAGE. The pH profile of maltooligosaccharide transferase activity coincided with that of the amylo-1,6-glucosidase activity (pH optimum at 6.0). The existence of GDE as well as glycogen phosphorylase in the brain explains brain glycogenolysis fully and supports the hypothesis that glycogen is a significant source of energy in this organ.

Animals↗
PubMed2005

[Mutation analysis of glycogen debrancher enzyme gene in five Chinese patients with glycogen storage disease type III].

OBJECTIVE: Type III glycogen storage disease (GSD-III, McKusick 232400), is a rare autosomal recessive disorder, also known as Cori's or Forbe's disease. The affected enzyme is amylo-1,6-glucosidase, 4-alpha-glucanotransferase (glycogen debrancher enzyme, GDE or amylogluco-sidase, AGL), which is responsible for the debranching of the glycogen molecule during catabolism. The AGL gene is located on chromosome 1p21 and contains 35 exons translated in a monomeric protein product. The clinical manifestations of GSD-III are represented by hepatomegaly, recurrent hypoglycemia, seizures, growth failure, dysmorphism, hyperlipidemia, raised transaminases and creatine kinase concentrations and, in a number of subjects, myopathy and cardiomyopathy. The hepatocellular adenoma, hepatocellular carcinoma, diabetes mellitus and liver fibrosis remain rare events. The diagnosis of debrancher deficiency was established by laboratory tests, electromyography (EMG), and muscle and liver biopsy. METHODS: We studied six GSD-III families after patients or parental consent and the clinical characteristics were documented. Analysis of 33 exons and part exon-intron boundaries of the AGL gene in patients and their parents were carried out by PCR and direct DNA sequencing. RESULTS: The clinical features included hepatomegaly, splenomegaly, recurrent hypoglycemia, hyperlipidemia, growth failure, raised transaminases and acidosis. Administration of epinephrine 2 hours after a carbohydrate meal could provoke normal rise of blood glucose in the affected individuals, but could not evoke any response after overnight fasting. Administration of raw-corn-starch could maintain normoglycemia and improve the disease condition. Mutation analysis for patient 1 was normal. Patient 2 had a compound heterozygote: a C-to-T transition at nucleotide 1294 (come from father, 1294C > T, L 298 L) in exon 8 and a G-to-T transition at nucleotide 4747 (from mother, 4747G > T, E1450X) in exon 34. Patient 3 had a compound heterozygote: a C-to-T transition at nucleotide 1294 (from father, 1294C > T, L 298 L) in exon 8 and a G-to-A transition at nucleotide -10 (from mother, -10G > A) in exon 3. Patient 4 was a homozygote: an insertion of a nucleotide CT into position +65 in exon 35 (4664 ins CT). Patient 5 had a compound heterozygote: a 8 bp deletion at nucleotide 2341 (from father, 2341delGCCATAGA, frameshift mutation) in exon 16 and a G-to-A transition at nucleotide 1559 (from mother, 1559G > A, R 387 Q) in exon 10. Patient 6 had a compound heterozygote: a T-to-G transition at nucleotide 1686 (from mother, 1686T > G, Y429 X) in exon 12 and a G-to-A transition at nucleotide 3742 (from father, 3742G > A, G 1115 R) in exon 26. CONCLUSION: GSD-III patients have variable phenotypic characteristics. Administration of raw-corn-starch can effectively improve the disease outcome. We identified 8 new mutations on AGL gene through nucleotide sequence analysis.

Child↗
PubMed1980

[Changes in the glycogen synthetase isoenzyme makeup and the formation of glycogen organelles in the liver of the developing rat embryo].

Glycogen synthetase of the rat embryo liver is represented until the 14th day of embryogenesis by the enzyme of "embryonic" (or so called muscle) type. This type is gradually replaced for an isozyme (isozymes) characteristic of the rat adult liver from the 15th till the 18th days of embryogenesis. The formation of glycogen organelles (glucosomes) in the embryonic liver occurs during the 18--19th day of development, i. e. after the full replacement of "embryonic" glycogen synthetase.

Animals↗
PubMed1987

Determination of glycogen and enzymes of glycogen metabolism in human hair follicles.

The skin epithelium and its organelles use glycogen as well as glucose as source of energy. Therefore the characterisation of glycogen metabolism and the enzymes involved is important in the study of mechanisms regulating the normal or abnormal differentiation of skin organelles such as sebaceous glands and hair follicles. The present paper describes fluorimetric methods for the determination of glycogen and for the measurements of phosphorylase and phosphorylase kinase activity in one and the same lysate of minute tissue samples. The methods were tested for their suitability on freshly isolated human hair follicles and cultured hair follicle cells. The possible use of these techniques for studies on the pathophysiology of acne and hirsutism is discussed.

Cells, Cultured↗
PubMed2004

Glycogen branching enzyme (GBE1) mutation causing equine glycogen storage disease IV.

Comparative biochemical and histopathological evidence suggests that a deficiency in the glycogen branching enzyme, encoded by the GBE1 gene, is responsible for a recently identified recessive fatal fetal and neonatal glycogen storage disease (GSD) in American Quarter Horses termed GSD IV. We have now derived the complete GBE1 cDNA sequences for control horses and affected foals, and identified a C to A substitution at base 102 that results in a tyrosine (Y) to stop (X) mutation in codon 34 of exon 1. All 11 affected foals were homozygous for the X34 allele, their 11 available dams and sires were heterozygous, and all 16 control horses were homozygous for the Y34 allele. The previous findings of poorly branched glycogen, abnormal polysaccharide accumulation, lack of measurable GBE1 enzyme activity and immunodetectable GBE1 protein, coupled with the present observation of abundant GBE1 mRNA in affected foals, are all consistent with the nonsense mutation in the 699 amino acid GBE1 protein. The affected foal pedigrees have a common ancestor and contain prolific stallions that are likely carriers of the recessive X34 allele. Defining the molecular basis of equine GSD IV will allow for accurate DNA testing and the ability to prevent occurrence of this devastating disease affecting American Quarter Horses and related breeds.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1989

An NADH-linked luciferase assay for glycogen: the preparation of glycogen-free, viable human eccrine sweat glands.

A glycogen assay based on bacterial NADH luciferase is described. It is free of tissue interference. The detection limit is 0.12 nmol glycogen, and the coefficient of variation is 5.5%. A method of depleting human eccrine sweat glands while retaining their viability is described. This depends on their incubation in 10(-5) M acetylcholine and 1 mM pyruvate. This method may be applicable to other tissues. The evidence for the viability of glycogen-depleted human eccrine sweat glands is reported and includes tissue contents of ATP and the rates of oxidation of glucose, pyruvate, beta-hydroxybutyrate, and palmitate.

Adenosine Triphosphate↗
PubMed1983

An hypothesis of function for the avian glycogen body: a novel role for glycogen in the central nervous system.

Our own and other recent data have led us to hypothesize that the glycogen body, heretofore generally considered to be metabolically inert, may be functionally geared to support the process of myelin formation in the avian central nervous system (CNS). We envision that the abundant glycogen stores in this tissue, unlike those in the liver or in skeletal muscle, can serve as a recyclable substrate for the ultimate production of reducing equivalents that would be available for the synthesis of myelin lipid cholesterol. In addition, it is suggested that such glycogen also may serve as a source of organic acids which might provide alternate substrates to the CNS under conditions of metabolic stress.

Animals↗
PubMed1970

Effects of glucose on glycogen synthetase, phosphorylase, and glycogen deposition in the perfused rat liver.

An increase in the perfusate glucose concentration from near zero to about 11 mM increased glycogen synthesis in the perfused, isolated rat liver from zero to a value about half the maximum seen in the intact animal. Increased synthesis appeard to due not only to provision of substrate but also to conversion of glycogen synthetase to the active form and of glycogen phosphorylase to the inactive form. These glucose effects, which are apparently independent of changes in levels of hormones or adenosine 3':5'-cyclic phosphate, may be physiologically significant for control of the blood glucose level.

Animals↗
PubMed2005

Crystal structure of an archaeal glycogen synthase: insights into oligomerization and substrate binding of eukaryotic glycogen synthases.

Glycogen and starch synthases are retaining glycosyltransferases that catalyze the transfer of glucosyl residues to the non-reducing end of a growing alpha-1,4-glucan chain, a central process of the carbon/energy metabolism present in almost all living organisms. The crystal structure of the glycogen synthase from Pyrococcus abyssi, the smallest known member of this family of enzymes, revealed that its subunits possess a fold common to other glycosyltransferases, a pair of beta/alpha/beta Rossmann fold-type domains with the catalytic site at their interface. Nevertheless, the archaeal enzyme presents an unprecedented homotrimeric molecular arrangement both in solution, as determined by analytical ultracentrifugation, and in the crystal. The C-domains are not involved in intersubunit interactions of the trimeric molecule, thus allowing for movements, likely required for catalysis, across the narrow hinge that connects the N- and C-domains. The radial disposition of the subunits confers on the molecule a distinct triangular shape, clearly visible with negative staining electron microscopy, in which the upper and lower faces present a sharp asymmetry. Comparison of bacterial and eukaryotic glycogen synthases, which use, respectively, ADP or UDP glucose as donor substrates, with the archaeal enzyme, which can utilize both molecules, allowed us to propose the residues that determine glucosyl donor specificity.

Adenosine Diphosphate Glucose↗
PubMed2001

Metabolic heterogeneity of glycogen in hepatocytes of patients with liver cirrhosis: the glycogen of the liver lobule zones in cirrhosis.

The concentrations of total glycogen (TG) and its labile (LF) and stable (SF) fractions were determined in hepatocytes of portal and central zones of the normal human liver and in the liver of patients with cirrhosis of viral and alcohol aetiologies. Using PAS reaction, TG, LF and SF were revealed in histological sections of the material obtained by the liver punch biopsies. The concentrations of TG and its fractions were measured by televisional cytophotometry. In liver cirrhosis, the concentrations of TG, LF and SF in both zones of the hepatic lobule have been found to be much higher than in the normal liver. It has been shown that the ratio of the hepatocyte TG concentrations in the portal zone to the central zone both in the normal liver and in viral cirrhosis exceeds 1.0, amounting to 1.264 +/- 0.021 and 1.030 +/- 0.009, respectively. The glycogen fraction composition in the cells of both the liver lobule zones in viral cirrhosis does not differ significantly from the norm. On the contrary, in the liver of patients with alcoholic cirrhosis, the ratio of the TG concentrations in the portal zone to the central zone is reduced to 0.815 +/- 0.016 and is accompanied by qualitative changes of the glycogen composition.

Biopsy, Needle↗
PubMed2002

Human skeletal muscle expresses a glycogen-targeting subunit of PP1 that is identical to the insulin-sensitive glycogen-targeting subunit G(L) of liver.

Insulin has been previously shown to regulate the expression of the hepatic glycogen-targeting subunit, G(L), of protein phosphatase 1 (PP1) and is believed to control the activity of the PP1-G(L) complex by modulation of the level of phosphorylase a, which allosterically inhibits the activity of PP1-G(L). These mechanisms contribute to the ability of insulin to increase hepatic glycogen synthesis. Human G(L) shows >88% amino acid identity to its rat and mouse homologs, with complete conservation of the phosphorylase a binding site. G(L) is highly expressed in the liver and present at appreciable levels in heart tissue of all three species. Surprisingly, G(L) is highly expressed in human skeletal muscle while only being detected at very low levels in rat, mouse, and rabbit skeletal muscle. The amino acid sequence of G(L) predicted from the cDNA is identical in human liver and skeletal muscle and encoded by a gene on chromosome 8 at p23.1. The species-specific difference in the level of expression of G(L) mRNA and protein in skeletal muscle has important implications for understanding the mechanisms by which insulin regulates glycogen synthesis in human skeletal muscle and for questions regarding whether rodents are appropriate models for this purpose.

Adult↗
PubMedDate not supplied

Ground glasslike hepatocytes produced by glycogen-membrane complexes ("glycogen bodies").

A 54-year-old man developed liver disease 11 months after renal transplantation. Liver biopsy demonstrated hepatitis with numerous periodic acid-Schiff-positive, diastase-sensitive ground glass inclusions in parenchymal cells. Electron microscopy revealed that the inclusions consisted of parallel arrays of smooth surfaced cisternae separated by glycogen rosettes ("glycogen bodies"). The differential diagnosis of ground glass hepatocytes, the occurrence of glycogen bodies, and the possible etiological factors in the patient's liver disease are discussed.

Cell Membrane↗
PubMed1983

The regulation of glycogen phosphorylase and glycogen breakdown in human skeletal muscle.

The regulation of glycogen phosphorylase and glycogen breakdown in human skeletal muscle has been investigated using the needle biopsy technique. Preliminary studies showed that the activity of phosphorylase in vitro was dependent upon the concentration of inorganic phosphate (Pi) used in the assay system. The Km of phosphorylase a for Pi was found to be 26.2 mmol/l, and that of (a+b) (assayed in the presence of saturating AMP) was 6.8 mmol/l. Because of the difference in Km the apparent percentage of a to (a+b) activity varies with the Pi concentration used in the assay system. Phosphorylase a and (a+b) activities were therefore adjusted to saturating Pi concentrations. The ratio of the activities in this case is independent of the Pi concentration and constitutes a minimal estimate of the fraction of phosphorylase molecules in the a form. The fraction of phosphorylase in the a form in resting muscle was as a mean 22%. Despite nearly a quarter of the phosphorylase being in the a form glycogenolytic activity is extremely low. It is proposed that the concentration of Pi at the active site of the enzyme is low compared to the Km for this of either form of the enzyme, and is limiting to activity. A Pi concentration in resting muscle of 1-3 mmol/l was calculated. During epinephrine infusion at rest 90% of the phosphorylase was transformed to the a form but only a moderate increase in the glycogenolytic rate occurred. This rate approximated to 5-10% of the maximum rate of the enzyme (Vmaxa). During prolonged epinephrine infusion the glycogenolytic rate decreased despite the continuance of 90% or more of the phosphorylase in the a form. In contrast to epinephrine infusion prolonged ischemia resulted in a decrease in the mole fraction of phosphorylase a and simultaneously in an increase of the glycogenolytic rate. During isometric and dynamic exercise there was a rapid transformation of phosphorylase b to a paralleled by pronounced increase in the rate of glycogen breakdown. The increased rate of glycogenolysis during isometric exercise was close to the Vmax of phosphorylase a in vivo. When either form of exercise was continued to fatigue/exhaustion, a re-transformation of phosphorylase a to b was observed. During dynamic exercise cAMP in the muscle increased two fold. This increase was blocked by the prior administration of propranolol.+

Acid-Base Equilibrium↗
PubMed1981

The accumulation of 2-deoxyglucose-6-phosphate activates glycogen synthase (and inactivates glycogen phosphorylase) in rat skeletal muscle.

In the muscle loaded with 2-dGlc "in vitro" (this sugar is accumulated as hexosephosphate) glycogen synthase I levels are changed by a mechanism which is additive to those of hormones such as insulinor epinephrine. The levels of glycogen phosphorylase are decreased only at the highest 2-dGlc-6-P concentration. The role of this effect of sugar phosphate - which has been attributed to the activation of muscle phosphatase (6) - is discussed with regard to glycogen metabolism during muscle function.

Animals↗