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At least 19 recordsLinked to original sources
PubMed2006

The experimental type 2 diabetes therapy glycogen phosphorylase inhibition can impair aerobic muscle function during prolonged contraction.

Glycogen phosphorylase inhibition represents a promising strategy to suppress inappropriate hepatic glucose output, while muscle glycogen is a major source of fuel during contraction. Glycogen phosphorylase inhibitors (GPi) currently being investigated for the treatment of type 2 diabetes do not demonstrate hepatic versus muscle glycogen phosphorylase isoform selectivity and may therefore impair patient aerobic exercise capabilities. Skeletal muscle energy metabolism and function are not impaired by GPi during high-intensity contraction in rat skeletal muscle; however, it is unknown whether glycogen phosphorylase inhibitors would impair function during prolonged lower-intensity contraction. Utilizing a novel red cell-perfused rodent gastrocnemius-plantaris-soleus system, muscle was pretreated for 60 min with either 3 micromol/l free drug GPi (n=8) or vehicle control (n=7). During 60 min of aerobic contraction, GPi treatment resulted in approximately 35% greater fatigue. Muscle glycogen phosphorylase a form (P<0.01) and maximal activity (P<0.01) were reduced in the GPi group, and postcontraction glycogen (121.8 +/- 16.1 vs. 168.3 +/- 8.5 mmol/kg dry muscle, P<0.05) was greater. Furthermore, lower muscle lactate efflux and glucose uptake (P<0.01), yet higher muscle Vo(2), support the conclusion that carbohydrate utilization was impaired during contraction. Our data provide new confirmation that muscle glycogen plays an essential role during submaximal contraction. Given the critical role of exercise prescription in the treatment of type 2 diabetes, it will be important to monitor endurance capacity during the clinical evaluation of nonselective GPi. Alternatively, greater effort should be devoted toward the discovery of hepatic-selective GPi, hepatic-specific drug delivery strategies, and/or alternative strategies for controlling excess hepatic glucose production in type 2 diabetes.

Animals↗
PubMed1986

Binding of vitamin B2 and its coenzyme forms by muscle glycogen phosphorylase b.

Binding of vitamin B2 and its coenzyme forms by glycogen phosphorylase b was studied by sedimentation velocity and sedimentation equilibrium methods. Microscopic dissociation constants for complexes of the enzyme with riboflavin, FMN and FAD were found to be 12.5, 6.8 and 18.1 microM, respectively (0.1 M KCl, pH 6.8, 20 degrees C). We revealed also that glucose 1-phosphate, glycogen and AMP decreased the affinity of the enzyme for FMN.

Adenosine Monophosphate↗
PubMed1986

A spectrophotometric study of vitamin B2 and its coenzyme forms binding to muscle glycogen phosphorylase b.

The vitamin B2 and its coenzyme forms binding to glycogen phosphorylase b from rabbit skeletal muscle has been studied by the spectrophotometric method. The spectral properties of riboflavin, FMN and FAD bound to muscle glycogen phosphorylase b were found to be identical at the wavelengths of 300 to 500 nm. According to data on spectrophotometric titration of muscle glycogen phosphorylase b by FMN, each subunit of the enzyme contains one flavin-binding site.

Animals↗
PubMed2006

Immunocytochemical analysis of rat vagus nerve by antibodies against glycogen phosphorylase isozymes.

Glycogen is an endogenous store of glucose equivalents for energy metabolism in many tissues. The brain contains a significant amount of glycogen the role of which as an energy reserve is currently under debate. Apparently little is known concerning a possible role of glycogen in peripheral nerves. We have demonstrated immunocytochemically the presence of glycogen phosphorylase (GP), a key enzyme in glycogen metabolism, in large and small axons of the rat vagus nerve, but not in Schwann cells. Furthermore, the isozyme-specific antibodies applied detected only the presence of the brain isoform BB of GP, but not the muscle isoform MM. This is in agreement with the occurrence of solely the BB isoform in the few brain and spinal cord neurons that contain GP. In contrast, astroglial cells in brain and spinal cord have previously been shown to contain both isoforms. Since GP isozymes are regulated differentially, the expression of isoform BB may provide hints to possible functions of glycogen in the vagus nerve.

Animals↗
PubMed2005

Crystallographic studies on acyl ureas, a new class of glycogen phosphorylase inhibitors, as potential antidiabetic drugs.

Acyl ureas were discovered as a novel class of inhibitors for glycogen phosphorylase, a molecular target to control hyperglycemia in type 2 diabetics. This series is exemplified by 6-{2,6-Dichloro- 4-[3-(2-chloro-benzoyl)-ureido]-phenoxy}-hexanoic acid, which inhibits human liver glycogen phosphorylase a with an IC(50) of 2.0 microM. Here we analyze four crystal structures of acyl urea derivatives in complex with rabbit muscle glycogen phosphorylase b to elucidate the mechanism of inhibition of these inhibitors. The structures were determined and refined to 2.26 Angstroms resolution and demonstrate that the inhibitors bind at the allosteric activator site, where the physiological activator AMP binds. Acyl ureas induce conformational changes in the vicinity of the allosteric site. Our findings suggest that acyl ureas inhibit glycogen phosphorylase by direct inhibition of AMP binding and by indirect inhibition of substrate binding through stabilization of the T' state.

Adenosine Monophosphate↗
PubMedDate not supplied

Kinetic analysis and modelling of the allosteric behaviour of liver and muscle glycogen phosphorylases.

Allosteric enzymes have very complex kinetic behaviours which are primarily interpreted through simplified models. To describe the functional properties of liver and muscle glycogen phosphorylase isozymes we have developed an experimental strategy based on the measurements of initial reaction rates in the presence of different concentrations of the effectors glucose-1-phosphate and methyl-xanthines. Using the extensive structural information available for the two glycogen phosphorylase conformers T (inactive) and R (active) with different ligands, we have applied the Monod-Wyman-Changeux model and analysed the results in the context of the exclusive binding of the inhibitors to the T state, meanwhile the substrate glucose-1-phosphate binds to both, the R and T states. The kinetic analysis shows a good agreement between our model and the results obtained from the glycogen phosphorylases and inhibitors included in this study, which demonstrates the validity of the approach described here.

Allosteric Regulation↗
PubMed2005

Modeling aided design of potent glycogen phosphorylase inhibitors.

Molecular modeling has been used to assist in the development of a novel series of potent glycogen phosphorylase inhibitors based on a phenyl diacid lead, compound 1. In the absence of suitable competitive binding assays, compound 1 was predicted to bind at the AMP allosteric site based on superposition onto known inhibitors which bind at different sites in the enzyme and analyses of the surrounding protein environment associated with these distinct sites. Possible docking modes of compound 1 at the AMP allosteric site were further explored using the crystal structure of rabbit muscle glycogen phosphorylase complexed with a Bayer diacid compound W1807 (PDB entry 3AMV). Compound 1 was predicted to interact with positively charged arginines at the AMP allosteric site in the docking model. Characterization of the binding pocket by a grid-based surface calculation of the docking model revealed a large unfilled hydrophobic region near the central phenyl ring, suggesting that compounds with larger hydrophobic groups in this region would improve binding. A series of naphthyl diacid compounds were designed and synthesized to access this hydrophobic cleft, and showed significantly improved potency.

Adenosine Monophosphate↗
PubMed2005

Glycogen phosphorylase isozyme pattern in mammalian retinal Müller (glial) cells and in astrocytes of retina and optic nerve.

Müller cells, the radially oriented dominant macroglial cells of the retina, are known to contain abundant glycogen as well as the key enzyme for its degradation, glycogen phosphorylase (GP), but the expressed isozyme pattern is unknown. To elucidate the isoform expression pattern, specific antisera directed against the brain (BB) and muscle (MM) isoforms of GP were applied to retinal sections, isolated Müller cells, and sections of the optic nerve. We show that Müller cells of rat, rabbit, guinea pig, and mouse retina exclusively express the BB isoform. Astrocytes of rat and rabbit optic nerve, as well as retina express only the BB isoform. In contrast, astrocytes in the brain and spinal cord as well as the epithelial cells of the pars caeca and of the ciliary body express both the BB and MM isoform. This result may indicate some differences in the role of glycogen in retinal macroglia and brain astrocytes, reflecting a local specialization of macroglia in the retina proper.

Animals↗
PubMed2005

Acyl ureas as human liver glycogen phosphorylase inhibitors for the treatment of type 2 diabetes.

Using a focused screening approach, acyl ureas have been discovered as a new class of inhibitors of human liver glycogen phosphorylase (hlGPa). The X-ray structure of screening hit 1 (IC50 = 2 microM) in a complex with rabbit muscle glycogen phosphorylase b reveals that 1 binds at the AMP site, the main allosteric effector site of the dimeric enzyme. A first cycle of chemical optimization supported by X-ray structural data yielded derivative 21, which inhibited hlGPa with an IC50 of 23 +/- 1 nM, but showed only moderate cellular activity in isolated rat hepatocytes (IC50 = 6.2 microM). Further optimization was guided by (i) a 3D pharmacophore model that was derived from a training set of 24 compounds and revealed the key chemical features for the biological activity and (ii) the 1.9 angstroms crystal structure of 21 in complex with hlGPa. A second set of compounds was synthesized and led to 42 with improved cellular activity (hlGPa IC50 = 53 +/- 1 nM; hepatocyte IC50 = 380 nM). Administration of 42 to anaesthetized Wistar rats caused a significant reduction of the glucagon-induced hyperglycemic peak. These findings are consistent with the inhibition of hepatic glycogenolysis and support the use of acyl ureas for the treatment of type 2 diabetes.

Adenosine Monophosphate↗
PubMed2002

Spontaneous "second wind" and glucose-induced second "second wind" in McArdle disease: oxidative mechanisms.

BACKGROUND: Blocked glycogen breakdown in McArdle disease impairs oxidative as well as anaerobic metabolism, but the contribution of impaired oxidative phosphorylation to everyday symptoms of McArdle disease remains poorly defined. OBJECTIVE: To evaluate the oxidative implications of the spontaneous second wind and variables that influence the development of this typical feature of McArdle disease. DESIGN: Assessment of exercise and oxidative capacity (.VO(2)) before and after the spontaneous "second wind" and with a glucose infusion after a spontaneous second wind. PATIENTS: Eight patients with complete myophosphorylase deficiency and 1 unique patient with 3% of normal myophosphorylase activity. MAIN OUTCOME MEASURES: Work capacity,.VO(2), heart rate, cardiac output. RESULTS: All patients with complete myophosphorylase deficiency (1) had low peak.VO(2) (mean +/- SD, 13.0 +/- 2.0 mL. kg(-1). min(-1)) in the first 6 to 8 minutes of exercise; (2) achieved a spontaneous second wind with increased exercise capacity between 8 and 12 minutes of exercise due to a more than 25% increase in peak.VO(2) (16.5 +/- 3.1 mL. kg(-1). min(-1)); and (3) with glucose infusion after a spontaneous second wind, experienced a further more than 20% increase in oxidative capacity (.VO(2), 19.9 +/- 3.9 mL. kg(-1). min(-1)). In the patient with residual myophosphorylase,.VO(2) (22.2 mL. kg(-1). min(-1)) in the first 6 to 8 minutes of exercise was approximately 2-fold higher than the mean of patients lacking myophosphorylase, and no significant improvement in exercise and oxidative capacity accompanied prolonged exercise or glucose infusion. CONCLUSIONS: First, the spontaneous second wind and the glucose-induced second second wind in McArdle disease are due to substrate-dependent increases in muscle oxidative capacity. Second, by providing glycogen-derived pyruvate, a small amount of residual myophosphorylase activity normalizes the oxidative deficit of complete myophosphorylase deficiency and virtually eliminates the spontaneous second wind and glucose-induced second second wind.

Adult↗
PubMed2003

Muscle glycogenosis and mitochondrial hepatopathy in an infant with mutations in both the myophosphorylase and deoxyguanosine kinase genes.

OBJECTIVES: To document 2 apparently incongruous clinical disorders occurring in the same infant: congenital myopathy with myophosphorylase deficiency (McArdle disease) and mitochondrial hepatopathy with liver failure and mitochondrial DNA depletion. METHODS: An infant girl born to consanguineous Moroccan parents had severe congenital hypotonia and hepatomegaly, developed liver failure, and died at 5 months of age. We studied muscle and liver biopsy specimens histochemically and biochemically, and we sequenced the whole coding regions of the deoxyguanosine kinase (dGK) and myophosphorylase (PYGM) genes. RESULTS: Muscle biopsy specimens showed subsarcolemmal glycogen accumulation and negative histochemical reaction for phosphorylase. Liver biopsy specimens showed micronodular cirrhosis and massive mitochondrial proliferation. Biochemical analysis showed phosphorylase deficiency in muscle and cytochrome c oxidase deficiency in liver. We identified a novel homozygous missense G-to-A mutation at codon 456 in exon 11 of PYGM, as well as a homozygous 4-base pair GATT duplication (nucleotides 763-766) in exon 6 of dGK, which produces a frame shift and a premature TGA stop codon at nucleotides 766 to 768, resulting in a truncated 255-amino acid protein. Both mutations were absent in 100 healthy individuals. CONCLUSIONS: Our data further expand the genetic heterogeneity in patients with McArdle disease; confirm the strong relationship between mitochondrial DNA depletion syndrome, liver involvement, and dGK mutations; and suggest that genetic "double trouble" should be considered in patients with unusual severe phenotypes.

Blotting, Southern↗
PubMed2004

A new rare mutation (691delCC/insAAA) in exon 17 of the PYGM gene causing McArdle disease.

OBJECTIVE: To investigate the genetic effect of a new mutation found in exon 17 of the myophosphorylase (PYGM) gene as a cause of McArdle disease (also known as type 5 glycogenosis). Patients A Spanish patient with McArdle disease was screened for 3 common mutations in the PYGM gene (R49X, W797R, and G204S), as previously described. The patient was heterozygous for R49X. To find other mutations, the coding sequence of the entire PYGM gene was sequenced. The carrier status of his relatives was also studied. RESULTS: A novel rare mutation was found in codon 691 of exon 17. This is an insertion/deletion (indel) and consists simultaneously of a deletion of 2 bases and an insertion of 3 bases (691delCC/insAAA). A restriction analysis was designed to simplify the detection method. CONCLUSIONS: The 691delCC/insAAA is the third indel described in the PYGM gene. Indels represent 0.95% of the total reported mutations in the Human Gene Mutation Database. The molecular origin of this mutation is not fully understood. These findings point again to the allelic heterogeneity of McArdle disease.

Adult↗
PubMed1999

A new mutation in the regulatory domain of the myophosphorylase gene affecting protein dimer contact.

We have identified a novel missense mutation in the myophosphorylase gene in a Spanish patient with McArdle's disease. The patient was homozygous for a T-to-C transition at codon 115 (L115P) in exon 3, which changed an encoded leucine (CUG) to a proline (CCG). This is the first mutation to be described in exon 3 and in a protein domain related to dimer contact. These data further emphasize the importance of private mutations in McArdle's disease, some of which are associated with specific ethnic groups.

Glycogen Phosphorylase, Muscle Form↗