The fine structure of glycogen from type IV glycogen-storage disease

Spatial Structure of Glycogen Molecules in Cells

Glycogen is a strongly branched polymer of α-D-glucose, with glucose residues in the linear chains linked by 1→4-bonds (~93% of the total number of bonds) and with branching after every 4-8 residues formed by 1→6-glycosidic bonds (~7% of the total number of bonds). It is thought currently that a fully formed glycogen molecule (β-particle) with the self-glycosylating protein glycogenin in the center has a spherical shape with diameter of ~42 nm and contains ~ 55,000 glucose residues. The glycogen molecule also includes numerous proteins involved in its synthesis and degradation, as well as proteins performing a carcass function. However, the type and force of bonds connecting these proteins to the polysaccharide moiety of glycogen are significantly different. This review presents the available data on the spatial structure of the glycogen molecule and its changes under various physiological and pathological conditions.

A Modified Enzymatic Method for Measurement of Glycogen Content in Glycogen Storage Disease Type IV

Deficiency of glycogen branching enzyme in glycogen storage disease type IV (GSD IV) results in accumulation of less-branched and poorly soluble polysaccharides (polyglucosan bodies) in multiple tissues. Standard enzymatic method, when used to quantify glycogen content in GSD IV tissues, causes significant loss of the polysaccharides during preparation of tissue lysates. We report a modified method including an extra boiling step to dissolve the insoluble glycogen, ultimately preserving the glycogen content in tissue homogenates from GSD IV mice. Muscle tissues from wild-type, GSD II and GSD IV mice and GSD III dogs were homogenized in cold water, and homogenate of each tissue was divided into two parts. One part was immediately clarified by centrifugation at 4°C (STD-prep); the other part was boiled for 5 min then centrifuged (Boil-prep) at room temperature. When glycogen was quantified enzymatically in tissue lysates, no significant differences were found between the STD-prep and the Boil-prep for wild-type, GSD II and GSD III muscles. In contrast, glycogen content for GSD IV muscle in the STD-prep was only 11% of that in the Boil-prep, similar to wild-type values. Similar results were observed in other tissues of GSD IV mice and fibroblast cells from a GSD IV patient. This study provides important information for improving disease diagnosis, monitoring disease progression, and evaluating treatment outcomes in both clinical and preclinical clinical settings for GSD IV. This report should be used as an updated protocol in clinical diagnostic laboratories.

Blood glucose response to rate of consumption of digestible carbohydrate

When the glycemic response to consuming digestible carbohydrate is measured, little or no attention appears to have been paid to the possible effect on this response of the rate at which the food is consumed. We compared glycemic responses when volunteers ate or drank foods containing digestible carbohydrate as rapidly as possible, or in five equal portions over 12 min. Expecting that the response would be greater when the food was consumed rapidly, we found that the responses were equally and randomly distributed between the two rates of eating. At the same time, marked differences were noted in the responses elicited when different individuals consumed the same foods, leading to an investigation of this phenomenon, published elsewhere.

How did glycogen structure evolve to satisfy the requirement for rapid mobilization of glucose? A problem of physical constraints in structure building

Optimization of molecular design in cellular metabolism is a necessary condition for guaranteeing a good structure-function relationship. We have studied this feature in the design of glycogen by means of the mathematical model previously presented that describes glycogen structure and its optimization function [Meléndez-Hevia et al. (1993), Biochem J 295: 477-483]. Our results demonstrate that the structure of cellular glycogen is in good agreement with these principles. Because the stored glucose in glycogen must be ready to be used at any phase of its synthesis or degradation, the full optimization of glycogen structure must also imply the optimization of every intermediate stage in its formation. This case can be viewed as a molecular instance of the eye problem, a classical paradigm of natural selection which states that every step in the evolutionary formation of a functional structure must be functional. The glycogen molecule has a highly optimized structure for its metabolic function, but the optimization of the full molecule has meaning and can be understood only by taking into account the optimization of each intermediate stage in its formation.

Enzyme activities of glycogen metabolism and mitochondrial characteristics in muscles of RN- carrier pigs (Sus scrofa domesticus)

High glycogen content and abnormal mitochondria have been seen in muscles from RN- carrier pigs in a previous work. Glycogen synthase, branching enzyme, phosphorylase and debranching enzyme activities, and mitochondrial characteristics were studied in normal and RN- carrier pigs. Branching enzyme activity was higher (P < 0.01) and glycogen synthase activity tended to be higher in longissimus dorsi muscle from RN- carrier pigs compared to normal pigs. There were no differences in the activities of either phosphorylase and debranching enzyme between both types of pigs. Citrate synthase activity and mitochondrial respiration were slightly higher in muscle from RN- pigs compared to normal pigs. Glycogen content in muscle from RN- pigs could result from the imbalance between anabolic and catabolic enzyme activities of glycogen metabolism. The higher specific activity in mitochondria of RN- pigs muscle might be the compensatory effect of an abnormal glycolytic metabolism.

Juvenile hereditary polyglucosan body disease with complete branching enzyme deficiency (type IV glycogenosis)

Polyglucosan body diseases in adults, contrary to infantile cases (Andersen's disease or type IV glycogenosis or amylopectinosis), are usually not associated with a significant deficiency of the branching enzyme (= amylo-1,4-1,6 transglucosidase). We, therefore, report on a 19-year-old male with complete branching enzyme deficiency presenting with severe myopathy, dilative cardiomyopathy, heart failure, dysmorphic features, and subclinical neuropathy. His 14-year-old brother had similar symptoms and was erroneously classified by a previous muscle biopsy as having central core disease but could later be identified as also having polyglucosan body myopathy. The skeletal muscle, endomyocardiac, and sural nerve biopsies as well as the autopsy revealed extraordinarily severe deposits of polyglucosan bodies not only in striated and smooth muscle fibers, but also in histiocytes, fibroblasts, perineurial cells, axons and astrocytes. Occasional paracrystalline mitochondrial inclusions were also noted. Thus, this patient represents to our knowledge the first juvenile, familial case of polyglucosan body disease with total branching enzyme deficiency and extensive polyglucosan body storage.

Regulation of lysosomal glycogen metabolism: studies of the actions of mammalian acid alpha-glucosidases

1. Acid alpha-glucosidases were purified to homogeneity from rat liver, rat skeletal muscle and human placenta. The properties of these enzymes were investigated. 2. Their pH optima for activity toward various substrates were in the range 4-5. 3. Time course and pH dependence experiments revealed that all glycogen substrates were not hydrolysed at the same rate; the rate of hydrolysis was inversely related to the molecular size of the substrate. The most rapidly hydrolysed glycogen substrate was the smallest (commercial oyster) while the least rapidly hydrolysed was the largest (native rat or rabbit liver). Intermediate sized glycogens were hydrolysed at intermediate rates. 4. Glycogen hydrolysis was stimulated by added sodium ions; this stimulation was pH dependent. 5. It is suggested that lysosomal glycogen metabolism may be controlled by pH, salt concentration and the size of the glycogen substrate. 6. Since the high molecular weight glycogen associated with lysosomes is formed by disulphide bridges between lower molecular weight material it is proposed that an important step of lysosomal glycogen degradation is disulphide bond reduction.

Polysaccharide storage myopathy

In a woman with a slowly progressive adult onset proximal myopathy, muscle biopsy showed storage of PAS positive material in type 1 fibers. This material consisted of a branched chain polysaccharide associated with a mucoprotein. No abnormality of glycogen-pathway enzymes was detected. This suggested that this polysaccharide accumulation occurred because the polysaccharide was laid down in a non-bioavailable form. The clinical and histochemical features in this patient and in the few similar reported cases indicate that polysaccharide storage myopathy is a distinct entity that is allied to the glycogen storage myopathies.

Enzymatic microanalysis of glycogen

A specific and simple enzymatic method for the determination of glycogen in tissue, with a detection limit of about 1 microgram glycogen (6.2 nmol glucosyl residues) is described. Glycogen is converted to 6-phosphogluconate by means of amyloglucosidase, hexokinase, and glucose-6-phosphate dehydrogenase. The increase in NADPH is measured fluorometrically. Muscle tissue (5-20 mg) is hydrolysed in hot KOH (5.4 mol/l), neutralized and analysed. The glycogen-glucosyl content in wet rat diaphragm muscle is about 43 mmol/kg.

Partial purification and properties of a bacterial isoamylase

Isoamylase has been prepared by affinity chromatography of a commercial enzyme-preparation from a strain of Cytophaga (also known as a Flavobacterium or Polyangium). The enzyme was not very stable, but the stability could be improved by calcium ions. The enzyme had a very low but significant activity on pullulan and on alpha-dextrins having maltosyl side-chains. This observation, which is contrary to previous reports, has been related to the specificity of isoamylase and other bacterial debranching-enzymes.

[The fine structure of trout liver glycogen]

1. The fine structure of trout liver glycogen has been investigated using an enzymatic method. 2. The total conversion of glycogen into glucose under the action of amyloglucosidase and the percentage of beta-amylolysis before (37.4%) and after (97.8%) isoamylase debranching are similar to the mammalian glycogen. 3. However, the resistance to beta-amylase of certain debranched material leads to an hypothesis during glycogenolysis.

Purification and properties of a debranching enzyme from Escherichia coli

The debranching enzyme (EC 3.2.1.-) from Escherichia coli K12 was purified 312-fold with a 21% yield, DEAE-cellulose and DEAE-Sephadex chromatography were used for purification. The preparation was homogeneous and showed only a single band of protein and activity upon polyacrylamide gel electrophoresis. The enzyme hydrolyzed 1,6-alpha-glucosidic linkages in phosphorylase and beta-amylase limit dextrins prepared from glycogen and amylopectin. Small branched oligosaccharides were also hydrolyzed. Amylopectin was also completely hydrolyzed but the enzyme showed only a very low activity with glycogen as the substrate. The enzyme cannot be classified as a pullulanase because it has practically no activity with pullulan. But it also differs from the bacterial isoamylases described in other studies because of its inability to hydrolyze glycogen. The optimal pH is about 5.6. The optimal growth conditions for the synthesis of the enzyme by E. coli were also examined in the present studies.

Type IV glycogenosis - a study of two cases

Liver biopsy materials of two siblings with type IV glycogenosis were studied by light and electron microscopy. Biochemical analysis was added using autopsy material in one of the two cases. Two kinds of polysaccharides were noted not only in the cardiac muscle, skeletal muscles, smooth muscles and reticuloendothelial cells, but also in the neutrophils and platelets. One was glycogen and the other was similar to amylopectin. Ultrastructurally, a large amount of fibrils, 60 A in width, glycogen rosettes and glycogen granules were detected in those cells. Branching glycosyltransferase deficiency was biochemically confirmed in one case examined.

Biochemical studies on tissues from a patient with Lafora disease

Tissues from the cerebral cortex, liver and myocardium of a patient with Lafora disease were obtained at autopsy and were studied biochemically. 1. Glucose content in the myocardium and liver was almost nil while that in the controls was 0.66 mg/g wet weight in the former and 8.80 mg/g wet weight in the latter. Glycogen content in the cerebral cortex and myocardium was about 10 and 3 times more than in controls. 2. Polyglucosan extracted from the cerebral cortex, liver and myocardium had a longer exterior glucose chain than that in the liver of the control but a normal, alpha or beta 1,4-glucosidic linkage was observed. 3. The activities of glucose-6-phosphatase and amylo-1,6-glucosidase in the cerebral cortex, liver and myocardium were well preserved. The activities of acid maltase in the three organs mentioned above and of neutral maltase in the myocardium were elevated twice and one and half times more than the control. Phosphorylase levels in the myocardium were extremely small, while in the cerebral cortex and liver normal activities were observed. In light of these findings, glycogen metabolism in Lafora disease is discussed.

Enzymic explorations of the structures of starch and glycogen

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