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At least 253 records · Page 14Linked to original sources
PubMed1995

Glycogen metabolism in the rat visceral yolk sac. 2. Activity of glycogen-degrading enzymes.

In an attempt to explain the previous observation of the rise and subsequent fall in glycogen content of the rat visceral yolk sac during the latter half of gestation, the activities of glycogen phosphorylase, glucose-6-phosphatase and lysosomal alpha-glucosidase were measured. Glycogen phosphorylase was found to be present in the yolk sac and, as in adult rat liver, was predominantly in the 'a' (active) form. The specific activity of the enzyme was lower than in adult rat liver, when expressed per mg tissue protein or per mg tissue wet weight, but similar when expressed per mg tissue glycogen. Phosphorylase activity in yolk sac was similar at 16.5 and 18.5 days of gestation. Glucose-6-phosphatase activity was not detectable in the yolk sac at either 15.5 or 18.5 days of gestation. Two lysosomal enzymes, acid alpha-glucosidase and N-acetyl-beta-hexosaminidase, were shown to be present in the yolk sac at higher specific activity than in adult liver. Alpha-Glucosidase activity in yolk sac was similar at 15.5 and 18.5 days of gestation. It is concluded that the net degradation of yolk sac glycogen initiated around 18.5 days of gestation does not serve to provide glucose for the fetus, and may indicate an increased demand for metabolic energy within the yolk sac itself.

Animals↗
PubMed1978

On the activities of glycogen phosphorylase and glycogen synthase in the liver of the rat.

A procedure was developed for determination of glycogen synthase and phosphorylase activities in liver after various in vivo physiological treatments. Liver samples were obtained from anaesthetised rats by freeze-clamping in situ. Other procedures were shown to stimulate the activity of phosphorylase and depress the activity of glycogen in the liver. The direction of glycogen metabolism appears to be regulated by the relative proportions of the two enzymes, as shown by a strong positive correlation between total activities and active forms of phosphorylase and synthase. The enzyme activities responded as expected to stimuli such as insulin and glucose, which depressed phosphorylase and increased synthase activity, and glucagon, which increased phosphorylase and decreased synthase activity. In fasted animals approximately 50% of each enzyme was in the active form, which suggests the existence of a potential futile cycle for glycogen metabolism. The role for such a cycle in the regulation of glycogen synthesis and degradation is discussed.

Animals↗
PubMed2004

Intermittent and recurrent hepatomegaly due to glycogen storage in a patient with type 1 diabetes: genetic analysis of the liver glycogen phosphorylase gene (PYGL).

We report a 19-year-old woman who had a history of type 1 diabetes with recurrent glycogen accumulation in the liver. During her infantile period she presented with no hepatomegaly nor growth retardation. On admission she was diagnosed with diabetic ketoacidosis (DKA). She also had hepatomegaly and elevated transaminase levels, but these abnormalities had resolved after administration of insulin. However, 4 weeks after DKA marked hepatomegaly and elevated transaminases were reappeared with simultaneous hypoglycemia which suggested an impaired glycogenolysis in the extraordinary conditions. We supposed the partial deficiency of liver glycogen phosphorylase activity in this patient and analyzed the liver glycogen phosphorylase gene (PYGL). Deduced amino acid sequence of the PYGL in this patient was completely identical to that reported by Burwinkel et al. (Y15233), however, the nucleotide sequence of PYGL cDNA was heterozygous for substitutions at positions Asp339 (GAT to GAC) on exon 9 and Ala703 (GCT to GCC on exon 17, respectively. These SNPs were also screened in 51 Japanese normal subjects by PCR-based direct sequencing or PCR-RFLP method. The same genotype observed in this patient was detected in 2 of 51(3.9%) normal subjects. These results suggest that the structure of PYGL coding sequence in this patient is unlikely to account for her excessive liver glycogen accumulation. Further studies including genetic analysis on the promoter region of the gene are necessary to clarify the etiology of susceptibility to excessive liver glycogen storage in patients with type 1 diabetes.

Adult↗
PubMed2006

Glucose utilization by the retinal pigment epithelium: evidence for rapid uptake and storage in glycogen, followed by glycogen utilization.

Glucose utilization and glycogen metabolism by human retinal pigment epithelium (RPE) cultures with high transepithelial resistance maintained on porous Millicell polycarbonate filters, were quantified by fluorophore-assisted carbohydrate electrophoresis (FACE). Glucose uptake was more efficient at the apical surface of the RPE. The utilization of glucose when restricted to either the apical or basal medium was also evaluated. Under both conditions, glucose was quickly transported to the opposite compartment and rapidly utilized. However, glucose from the apical compartment was depleted to a greater extent than from the basal compartment. The de novo synthesis and accumulation of glycogen accompanied glucose utilization. This was paralleled by a concomitant increase in lysosomal glycogen degradation measured as an increase in cell-associated maltodextrins. The highest levels of glucose in glycogen and maltodextrins occurred at 24 h, declining to basal levels at 72 h. Glucose transporter expression in the RPE cultures was evaluated with the reverse transcriptase-polymerase chain reaction. Glucose transporter-1 (GLUT 1) was the isoform expressed in these cells. GLUT 1 localization was determined by immunocytochemistry. GLUT 1 localizes to the apical and basolateral border of the RPE. The intensity of fluorescence was higher on the apical border. The rapid depletion of medium glucose suggests that RPE culture studies should replenish medium glucose more frequently than every 72 h to maintain physiologically relevant glucose concentrations. These studies are the first to demonstrate glucose, glycogen and maltodextrin metabolism by RPE cells, and their detection and quantitation by FACE.

Aminoacridines↗
PubMed1998

Identification of the separate domains in the hepatic glycogen-targeting subunit of protein phosphatase 1 that interact with phosphorylase a, glycogen and protein phosphatase 1.

Deletion and mutational analyses of the rat liver glycogen-targeting subunit (GL) of protein phosphatase 1 (PP1) have identified three separate domains that are responsible for binding of PP1, glycogen and phosphorylase a. The glycogen-binding domain spans the centre of GL between residues 144 and 231 and appears to be distinct from the glycogen-binding (storage) site of phosphorylase. The regulatory high-affinity binding site for phosphorylase a lies in the 16 amino acids at the C-terminus of GL. The PP1-binding domain is deduced to comprise the -RVXF- motif [Egloff, Johnson, Moorhead, Cohen and Barford (1997) EMBO J. 16, 1876-1887] located at residues 61-64 of GL and preceding lysine residues at positions 56, 57 and 59. A possible approach for increasing glycogen synthesis in certain disorders is discussed.

Amino Acid Sequence↗
PubMed2000

Insulin-stimulated phosphorylation of the protein phosphatase-1 striated muscle glycogen-targeting subunit and activation of glycogen synthase.

Protein phosphatase-1 (PP-1) in heart and skeletal muscle binds to a glycogen-targeting subunit (G(M)) in the sarcoplasmic reticulum. Phosphorylation of G(M) has been postulated to govern activity of PP1 in response to adrenaline and insulin. In this study, we used biochemical assays and G(M) expression in living cells to examine the effects of insulin on the phosphorylation of G(M), and the binding of PP-1 to G(M). We also assayed glycogen synthase activation in cells expressing wild type G(M) and G(M) mutated at the phosphorylation sites. In biochemical assays kinase(s) prepared from insulin-stimulated Chinese hamster ovary (CHO-IR) cells and C2C12 myotubes phosphorylated a glutathione S-transferase (GST) fusion protein, GST-G(M)(1-240), at both site 1 (Ser(48)) and site 2 (Ser(67)). Phosphorylation of both sites was dependent on activation of the mitogen-activated protein kinase pathway, involving in particular ribosomal protein S6 kinase. Full-length G(M) was expressed in CHO-IR cells and metabolic (32)P labeling at sites 1 and 2 was increased by insulin treatment. The G(M) expressed in CHO-IR cells or in C2C12 myotubes co-immunoprecipitated endogenous PP-1, and association was transiently lost following treatment of the cells with insulin. In contrast PP-1 binding to G(M)(S67T), a version of G(M) not phosphorylated at site 2, was unaffected by insulin treatment. Expression of G(M) increased basal activity of endogenous glycogen synthase in CHO-IR cells. Insulin stimulated glycogen synthase activity the same extent in cells expressing wild type G(M) or G(M) mutated to eliminate phosphorylation site 1 and/or site 2. Phosphorylation of G(M) is stimulated by insulin, but this phosphorylation is not involved in insulin control of glycogen metabolism. We speculate that other functions of G(M) at the sarcoplasmic reticulum membrane might be affected by insulin.

Animals↗
PubMed1980

Glycogen synthase from rabbit skeletal muscle. Amino acid sequence at the sites phosphorylated by glycogen synthase kinase-3, and extension of the N-terminal sequence containing the site phosphorylated by phosphorylase kinase.

Glycogen synthase kinase-3 phosphorylates three serine residues on glycogen synthase (sites 3a, 3b and 3c) which are all located in the same nine-amino-acid segment of the polypeptide chain. The sequence in this region is: Arg-Tyr-Pro-Arg-Pro-Ala-Ser(P)-Val-Pro-Pro-Ser(P)-Pro-Ser-Leu-Ser(P)-Arg-. These serine residues are distinct from the sites phosphorylated preferentially by cyclic-AMP-dependent protein kinase (sites 1a and 1b) and phosphorylase kinase (site 2). The N-terminal sequence of glycogen synthase containing the serine residue phosphorylated by phosphorylase kinase has been extended. The sequence in this region is: Pro-Leu-Ser-Arg-Thr-Leu-Ser(P)-Val-Ser-Ser-Leu-Pro-Gly-Leu-Glu-Asp-Trp-Glu-Asp- Glu-Phe-Asp-Leu-Glu-Asn-Ser-Val-Leu-Phe-(Asx2,Glx2,Ala2,Val2,Lys)-. The similarity to the N-terminal sequence of phosphorylase is confined to the immediate vicinity of the phosphorylation site (residues 4--15). The relationship of glycogen synthase kinase-3 to glycogen synthase kinases that have been described by other laboratories is discussed.

Amino Acid Sequence↗
PubMed1997

Insulin activates protein kinase B, inhibits glycogen synthase kinase-3 and activates glycogen synthase by rapamycin-insensitive pathways in skeletal muscle and adipose tissue.

Insulin stimulated protein kinase B alpha (PKB alpha) more than 10-fold and decreased glycogen synthase kinase-3 (GSK3) activity by 50 +/- 10% in skeletal muscle and adipocytes. Rapamycin did not prevent the activation of PKB, inhibition of GSK3 or stimulation of glycogen synthase up to 5 min. Thus rapamycin-insensitive pathways mediate the acute effect of insulin on glycogen synthase in the major insulin-responsive tissues. The small and very transient effects of EGF on phosphatidylinositol (3,4,5)P3 PKB alpha and GSK3 in adipocytes, compared to the strong and sustained effects of insulin, explains why EGF does not stimulate glucose uptake or glycogen synthesis in adipocytes.

Adipose Tissue↗
PubMed1990

Immunoblot analyses of glycogen debranching enzyme in different subtypes of glycogen storage disease type III.

To determine the tissue distribution of glycogen debranching enzyme, we used immunoblot analysis with a polyclonal antibody prepared against purified porcine muscle debranching enzyme. Debranching enzyme was identified in porcine brain, kidney, cardiac muscle, skeletal muscle, liver, and spleen; and in human liver, skeletal muscle, lymphocytes, lymphoblastoid cells, skin fibroblasts, cultured chorionic villi, and amniocytes. In each of these tissues the debranching enzyme band was 160 kd. To determine the molecular basis for glycogen storage disease type III at the protein level, tissues from 41 patients with glycogen storage disease type III were also subjected to immunoblot analysis. Three patients having isolated transferase deficiency with retention of glucosidase activity (type IIID disease) had nearly normal amounts of cross-reactive material. In the remaining patients (both transferase and glucosidase deficiency), debranching enzyme was either absent or greatly reduced. These latter patients included 31 with disease that appeared to involve both liver and muscle (type IIIA), four with disease that was present only in the liver (type IIIB), and three with unknown muscle status. In patients with both type IIIA and type IIIB disease, debranching enzyme protein was absent in skin fibroblasts, lymphoblastoid cells, and lymphocytes. The parents of two patients with type IIIA disease had an intermediate level of debranching enzyme protein, consistent with their presumed heterozygote state. An immunoblot analysis of cultured amniotic fluid cells from a woman whose fetus was at risk for type IIIA disease predicted an unaffected fetus; the prediction was confirmed postnatally. Thus Western blot analysis offers an alternate method of prenatal diagnosis for the most common form of glycogen storage disease type III.

Blotting, Western↗
PubMed1984

Effect of prolonged starvation on glycogen synthase and glycogen synthase phosphatase activity in rat heart.

Rats were fasted 24, 48 or 72 hours to determine the effect of several days without food on glycogen synthase and synthase phosphatase activity in heart. The basal percentage of synthase I decreased gradually from approximately 20% in fed animals to approximately 6% in rats starved for 72 hours. Glycogen increased progressively from 4.6 mg/g wet weight in fed rats to 7.6 mg/g wet weight in 72-hour starved rats. Thus, there was an inverse relationship between the glycogen concentration and the basal percentage of synthase I. The total synthase phosphatase activity measured at a standardized glycogen concentration decreased 50% by 24 hours of starvation and then was unchanged up to 72 hours. The 50% decrease in phosphatase activity correlated directly with insulin concentration in rats fasted 24-72 hours. The rapid stimulatory effect of insulin on synthase activity observed in fed rats was delayed in rats starved 24 and 48 hours. This correlated with a progressively slower synthase phosphatase response to insulin. The stimulatory effect of insulin was lost completely in 72-hour fasted rats. The proposed mechanism for the delayed response in rats starved 24 and 48 hours and lack of response in rats starved 72 hours is insulin resistance. The mechanism remains to be elucidated.

Animals↗
PubMed1987

The polymorphic locus for glycogen storage disease VI (liver glycogen phosphorylase) maps to chromosome 14.

Human liver glycogen phosphorylase deficiency, also known as glycogen storage disease type VI (GSD VI) or Hers disease, is characterized by hepatomegaly and reduced or absent glycogenolytic response to the injection of glucagon. The recently isolated cDNA encoding the liver isozyme of glycogen phosphorylase was used to map the gene and identify restriction-fragment polymorphisms in normal Caucasians as a prerequisite for detecting linked GSD VI abnormalities. Results of restriction-enzyme analysis using a downstream fragment of the liver glycogen phosphorylase cDNA indicated the existence of a single gene copy per haploid genome. Hybridization of this downstream liver phosphorylase probe to dual laser-excited, sorted human chromosomes localized the gene to human chromosome 14. When the downstream probe was tested on genomic DNA cut with seven different restriction enzymes, a single MspI restriction-fragment-length polymorphism (RFLP) was observed in a single individual. In contrast, similar Southern blots performed with an upstream portion of the cDNA encoding liver phosphorylase revealed common RFLPs for four of eight enzymes tested, with minor polymorphic allele frequencies ranging from 33% to 44%. One of the four enzymes (TaqI) revealed two independent polymorphisms. If random distribution of these haplotypes among normal and disease loci, is assumed, approximately 92% of fetuses at risk for Hers disease will be informative when tested with the upstream liver phosphorylase probe.

Chromosome Mapping↗
PubMed1997

Relationship of glycogen synthase and glycogen phosphorylase to protein phosphatase 2C and cAMP-dependent protein kinase in liver of obese rhesus monkeys.

The regulation of glycogen synthase (GS) and glycogen phosphorylase (GP) activity by phosphorylation/ dephosphorylation has been proposed to be via changes in activities of several different protein (serine/threonine) phosphatases and kinases, including protein phosphatase (PP) 1/2A, PP2C, and cAMP-dependent protein kinase (PKA). In order to determine whether PP1/2A, PP2C, and/or PKA activities are related to GS and/or GP activities, these enzymes were measured in freeze-clamped liver biopsies obtained under basal fasting conditions from 16 obese monkeys. Four monkeys were normoglycemic and normoinsulinemic, five were hyperinsulinemic, and seven had type 2 diabetes (NIDDM). Liver glycogen and glucose 6-phosphate (G6P) contents were also determine. Basal enzyme activities and basal substrate concentrations were not significantly different between the three group of obese monkeys; however, there were several significant linear relationships observed when the monkeys were treated as one group. Therefore, multiple regression was used to determine the correlation between key variables. GS fractional activity was correlated to GP fractional activity (p < 0.05) and to PP2C activity (p = 0.005) (adjusted R2, 53%). GP independent activity was correlated to GS independent activity (p < 0.07) and to PKA fractional activity (p = 0.005) (adjusted R2, 64%). PP2C activity was correlated to GS fractional activity (p < 0.0005) and to PP1/2A activity (p < 0.0001) (adjusted R2, 83%). PKA fractional activity was correlated to GP total activity (p < 0.0005) and to age (p = 0.001) (adjusted R2, 82%). G6P content was correlated to glycogen content (p < 0.05) and to PP2C activity (p = 0.0005) (adjusted R2, 73%). In conclusion, PP2C and PKA are involved in the regulation of GS and GP activity in the basal state in liver of obese monkeys with a wide range of glucose tolerance.

Animals↗
PubMed2000

Heterogeneous mutations in the glycogen-debranching enzyme gene are responsible for glycogen storage disease type IIIa in Japan.

Glycogen storage disease type IIIa (GSD IIIa) is an autosomal recessive disorder caused by deficiency of the glycogen-debranching enzyme (AGL). Recent studies of the AGL gene have revealed the prevalent mutations in North African Jewish and Caucasian populations, but whether these common mutations are present in other ethnic groups remains unclear. We have investigated eight Japanese GSD IIIa patients from seven families and identified seven mutations, including one splicing mutation (IVS 14+1G-->T) previously reported by us, together with six novel ones: a nonsense mutation (L124X), a splice site mutation (IVS29-1G-->C), a 1-bp deletion (587delC), a 2-bp deletion (4216-4217delAG), a 1-bp insertion (2072-2073insA), and a 3-bp insertion (4735-4736insTAT). The last mutation results in insertion of a tyrosine residue at a putative glycogen-binding site, and the rest are predicted to cause synthesis of truncated proteins lacking the glycogen-binding site at the carboxyl terminal. Thirteen novel polymorphisms have also been revealed in this study: three amino acid substitutions (R387Q, G1115R, and E1343 K), one silent point mutation (L298L), one nucleotide change in the 5'-noncoding region, and eight nucleotide changes in introns. Haplotype analysis with combinations of these polymorphic markers showed L124X, IVS14+1G-->T, and 4216-4217delAG to be on different haplotypes. These results demonstrate the importance of the integrity of the carboxy terminal domain in the AGL protein and the molecular heterogeneity of GSD IIIa in Japan.

Amino Acid Sequence↗
PubMed1996

Effects of temperature shifts on the activities of Neurospora crassa glycogen synthase, glycogen phosphorylase and trehalose-6-phosphate synthase.

Conidiospore germlings of Neurospora crassa submitted to a heat shock at 45 degrees C accumulate trehalose and degrade glycogen. The opposite occurs upon reincubation at a physiologic temperature (30 degrees C). These observations suggest a temperature-dependent mechanism for the preferential synthesis of one or the other sugar reserve. Here we show that concomitant with these shifts of temperature, occurred reversible changes in the activities of glycogen synthase and phosphorylase. Glycogen synthase was inactivated at 45 degrees C while phosphorylase was activated. The reverse was true when the cells were shifted back to 30 degrees C. Addition of cycloheximide did not prevent the reversible enzymatic changes, which remained stable after gel filtration. Apparently, the effects of temperature shifts occurred at the level of reversible covalent enzymatic modifications. Trehalose-6-phosphate synthase properties were also affected by temperature. For instance, the enzyme was less sensitive to in vitro inhibition by inorganic phosphate at 50 degrees C than at 30 degrees C. Fructose-6-phosphate partially relieved the inhibitory effect of phosphate at 30 degrees C but not at 50 degrees C. These effects of the assay temperature, inorganic phosphate, and fructose-6-phosphate, on trehalose-6-phosphate synthase activity, were more evident for crude extracts obtained from heat-shocked cells. Altogether, these results may contribute to explain the preferential accumulation of trehalose 45 degrees C, or that of glycogen at 30 degrees C.

Cycloheximide↗
PubMed1976

Regulation of rat liver glycogen synthesis and activities of glycogen cycle enzymes by glucose and galactose.

Direct regulation of rat liver glycogen metabolism by glucose and galactose was studied using an isolated liver perfusion system. Activation of glycogen synthase and net glycogen synthesis increased linearly when perfusate glucose concentration was increased from 125 to 500 mg/100 ml. Galactose, rapidly taken up by isolated rat liver regardless of circulating glucose concentration, increased these responses to glucose. In the presence of galactose (greater than or equal to 5 mg/100 ml), activation of synthase and glycogen synthesis were 1.5-fold higher at any given glucose concentration. The addition of insulin did not appreciably after synthase activation by glucose and galactose. Phosphorylase activity, low at circulating glucose levels above 125 mg/100 ml, was further decreased as glucose was increased or when galactose was added to the perfusate. Release of glucose into the perfusate in response to aglycemia was increased in the presence of galactose.

Animals↗
PubMed1989

Inhibitory effect of polycations on phosphorylation of glycogen synthase by glycogen synthase kinase 3.

Several polycations were tested for their abilities to inhibit the activity of glycogen synthase kinase 3 (GSK-3). L-Polylysine was the most powerful inhibitor of GSK-3 with half-maximal inhibition of glycogen synthase phosphorylation occurring at approx. 100 nM. D-Polylysine and histone H1 were also inhibitory, but the concentration dependence was complex, and DL-polylysine was the least effective inhibitor. Spermine caused about 50% inhibition of GSK-3 at 0.7 mM and 70% inhibition at 4 mM. Inhibition of GSK-3 by L-polylysine could be blocked or reversed by heparin. A heat-stable polycation antagonist isolated from swine kidney cortex also blocked the inhibitory effect of L-polylysine on GSK-3 and blocked histone H1 stimulation of protein phosphatase 2A activity. Under the conditions tested, L-polylysine also inhibited GSK-3 catalyzed phosphorylation of type II regulatory subunit of cAMP-dependent protein kinase and a 63 kDa brain protein, but only slightly inhibited phosphorylation of inhibitor 2 or proteolytic fragments of glycogen synthase that contain site 3 (a + b + c). L-Polylysine at a concentration (200 nM) that caused nearly complete inhibition of GSK-3 stimulated casein kinase I and casein kinase II, but had virtually no effect on the catalytic subunit of cAMP-dependent protein kinase. These results suggest that polycations can be useful in controlling GSK-3 activity. Polycations have the potential to decrease the phosphorylation state of glycogen synthase at site 3, both by inhibiting GKS-3 as shown in this study and by stimulating the phosphatase reaction as shown previously (Pelech, S. and Cohen, P. (1985) Eur. J. Biochem. 148, 245-251).

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1998

Two new mutations in the 3' coding region of the glycogen debranching enzyme in a glycogen storage disease type IIIa Ashkenazi Jewish patient.

Glycogen storage disease type III (GSD III) is an autosomal recessive disease caused by the deficiency of glycogen debranching enzyme (AGL). We report the finding of two new mutations in a GSD IIIa Ashkenazi Jewish patient. Both mutations are insertion of an adenine into a stretch of 8 adenines towards the 3' end of the coding region, one at position 3904 (3904insA) in exon 30, the second at position 4214 (4214insA) in exon 32. The mutations cause frameshifts and premature terminations of the glycogen debranching enzyme, the first causing a frameshift at amino acid 1304, the second causing a frameshift at amino acid 1408 of the total of 1532. These mutations demonstrate the importance of the 125 amino acids at the carboxy-terminus of the debrancher enzyme for its activity and support the suggestion that the putative glycogen binding domain is located in the carboxy-terminus of the AGL. The mutations cause distinctive single-strand conformation polymorphism (SSCP) patterns enabling easy detection.

Child, Preschool↗
PubMed2001

Intracellular distribution of glycogen synthase and glycogen in primary cultured rat hepatocytes.

Changes in the intracellular distribution of liver glycogen synthase (GS) might constitute a new regulatory mechanism for the activity of this enzyme at cellular level. Our previous studies indicated that incubation of isolated hepatocytes with glucose activated GS and resulted in its translocation from a homogeneous cytosolic distribution to the cell periphery. These studies also suggested a relationship with insoluble elements of the cytoskeleton, in particular actin. Here we show the translocation of GS in a different experimental model that allows the analysis of this phenomenon in long-term studies. We describe the reversibility of translocation of GS and its effect on glycogen distribution. Incubation of cultured rat hepatocytes with glucose activated GS and triggered its translocation to the hepatocyte periphery. The relative amount of the enzyme concentrated near the plasma membrane increased with time up to 8 h of incubation with glucose, when the glycogen stores reached their maximal value. The lithium-induced covalent activation of GS was not sufficient to cause its translocation to the cell periphery. The intracellular distribution of GS closely resembled that of glycogen. Our results showed an interaction between GS and an insoluble element of the hepatocyte matrix. Although no co-localization between actin filaments and GS was observed in any condition, disruption of actin cytoskeleton resulted in a significantly lower percentage of cells in which the enzyme translocated to the cell periphery in response to glucose. This observation suggests that the microfilament network has a role in the translocation of GS.

Animals↗