scholarly journals Association of glycogen synthase phosphatase and phosphorylase phosphatase activities with membranes of hepatic smooth endoplasmic reticulum.

1979 ◽  
Vol 83 (2) ◽  
pp. 348-356 ◽  
Author(s):  
R N Margolis ◽  
R R Cardell ◽  
R T Curnow
Keyword(s):  
Endoplasmic Reticulum ◽  
Glycogen Synthase ◽  
Close Contact ◽  
Smooth Endoplasmic Reticulum ◽  
Glycogen Synthesis ◽  
Glycogen Metabolism ◽  
Hepatic Glycogen ◽  
Phosphatase Activities ◽  
Regulatory Enzymes ◽  
Glycogen Particles

A detailed investigation was conducted to determine the precise subcellular localization of the rate-limiting enzymes of hepatic glycogen metabolism (glycogen synthase and phosphorylase) and their regulatory enzymes (synthase phosphatase and phosphorylase phosphatase). Rat liver was homogenized and fractionated to produce soluble, rough and smooth microsomal fractions. Enzyme assays of the fractions were performed, and the results showed that glycogen synthase and phosphorylase were located in the soluble fraction of the livers. Synthase phosphatase and phosphorylase phosphatase activities were also present in soluble fractions, but were clearly identified in both rough and smooth microsomal fractions. It is suggested that the location of smooth endoplasmic reticulum (SER) within the cytosome forms a microenvironment within hepatocytes that establishes conditions necessary for glycogen synthesis (and degradation). Thus the location of SER in the cell determines regions of the hepatocyte that are rich in glycogen particles. Furthermore, the demonstration of the association of synthase phosphatase and phosphorylase phosphatase with membranes of SER may account for the close morphological association of SER with glycogen particles (i.e., disposition of SER membranes brings the membrane-bound regulatory enzymes in close contact with their substrates).

Is Smooth Endoplasmic Reticulum Involved in Hepatic Glycogen Synthesis in the Fetal Mouse?

1985 ◽  
Vol 43 ◽  
pp. 496-497
Author(s):  
Joanette S. Breslin ◽  
Robert R. Cardell
Keyword(s):  
Endoplasmic Reticulum ◽  
Time Course ◽  
Smooth Endoplasmic Reticulum ◽  
Periodic Acid ◽  
Glycogen Synthesis ◽  
Microscopic Analysis ◽  
Hepatic Glycogen ◽  
Periodic Acid Schiff ◽  
Glycogen Deposition ◽  
Glycogen Particles

Considerable evidence suggests that hepatic smooth endoplasmic reticulum (SER) functions in both glycogen deposition and depletion and is closely associated with glycogen particles during both processes in the adult rodent liver. In this study we have investigated the time course of hepatic glycogen deposition and examined the association of SER with glycogen particles during fetal glycogen synthesis, i.e., from day 15 to day 19 of gestation (plug day = day 1).Livers were removed from fetal ICR mice and processed for either light (LM) and electron microscopy (EM) or biochemical determination of glycogen. Biochemical analysis of glycogen concentrations in each liver revealed an average of 0.1% glycogen in day 15 and day 16 fetal livers, 0.6% in those from day 17, 2.0% on day 18 and nearly 5.0% by day 19. Light microscopic analysis of periodic acid-Schiff (PAS) stained semi-thin (1.0μm) sections confirmed the presence of increasing amounts of glycogen beginning on day 16 and reaching a maximum on day 19 of gestation.

Morphometric analysis and autoradiography of the smooth endoplasmic reticulum during glycogen deposition in the fetal mouse hepatocyte

1990 ◽  
Vol 48 (3) ◽  
pp. 544-545
Author(s):  
Joanette Shockey Breslin ◽  
Robert R. Cardell
Keyword(s):  
Endoplasmic Reticulum ◽  
Morphometric Analysis ◽  
Smooth Endoplasmic Reticulum ◽  
Glycogen Synthesis ◽  
Glycogen Metabolism ◽  
Hepatic Glycogen ◽  
Thin Sections ◽  
Glycogen Accumulation ◽  
Fetal Mouse ◽  
Glycogen Deposition

Analyses of adult hepatic glycogen deposition by numerous investigators have determined that the smooth endoplasmic reticulum (SER) proliferates immediately prior to glycogen deposition and during the early stages of glycogen accumulation, then decreases as glycogen levels reach their maximum, suggesting that SER participates in adult hepatic glycogen metabolism. Less is known regarding fetal hepatic glycogen synthesis and the participation of the fetal SER. The studies described here test the hypothesis that the SER functions in the synthesis of fetal hepatic glycogen. Quantitative analysis of SER and glycogen levels during hepatic glycogen synthesis tests the existence of a correlation between glycogen and SER. Newly deposited labeled glycogen is localized via autoradiography and the extent of association between labeled glycogen and SER quantified, establishing whether glycogen is necessarily deposited near membranes of SER.Fetal mouse livers were harvested at daily intervals between days 14 and 19 of gestation, immersion fixed in 2% glutaraldehyde, 2% paraformaldehyde, post-fixed in 1 % OsO4 dehydrated in EtOH and embedded in Epon 812. Semi-thin (0.5μm) and ultra-thin sections (60 nm) were prepared for morphometric analysis.2

scholarly journals High-affinity binding of glycogen-synthase phosphatase to glycogen particles in the liver. Role of glycogen in the inhibition of synthase phosphatase by phosphorylase a

1987 ◽  
Vol 246 (2) ◽  
pp. 367-374 ◽  
Author(s):  
L Mvumbi ◽  
W Stalmans
Keyword(s):  
Endoplasmic Reticulum ◽  
High Speed ◽  
Glycogen Synthase ◽  
Smooth Endoplasmic Reticulum ◽  
Active Form ◽  
Glycogen Concentration ◽  
High Affinity ◽  
Glycogen Particles

1. Post-mitochondrial supernatants were prepared from the livers of 24 h-fasted rats. Upon centrifugation at high speed, the major part of the glycogen-synthase phosphatase activity sedimented with the microsomal fraction. However, two approaches showed that the enzyme was associated with residual glycogen rather than with vesicles of the endoplasmic reticulum. Indeed, the activity was entirely solubilized when the remaining glycogen was degraded either by glucagon treatment in vivo or by alpha-amylolysis in vitro. No evidence could be found for an association of glycogen-synthase phosphatase with the smooth endoplasmic reticulum, as isolated with the use of discontinuous sucrose gradients. 2. After solubilization by glucagon treatment in vivo, synthase phosphatase could be transferred to glycogen particles with very high affinity. Half-maximal binding occurred at a glycogen concentration of about 0.25 mg/ml, whereas glycogen synthase and phosphorylase required 1.5-2 mg/ml. 3. In gel-filtered extracts prepared from glycogen-depleted livers, the activation of glycogen synthase was not inhibited at all by phosphorylase alpha. The inhibition was restored when the liver homogenates were prepared in a glycogen-containing buffer. The effect was half-maximal at a glycogen concentration of about 0.25 mg/ml, and virtually complete at 1 mg/ml. These findings explain long-standing observations that in fasted animals the liver contains appreciable amounts of both synthase and phosphorylase in the active form.

scholarly journals Storage and Utilization of Glycogen by Mouse Liver during Adaptation to Nutritional Changes Are GLP-1 and PASK Dependent

Nutrients ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 2552
Author(s):  
Ana Pérez-García ◽  
Verónica Hurtado-Carneiro ◽  
Carmen Herrero-De-Dios ◽  
Pilar Dongil ◽  
José Enrique García-Mauriño ◽  
...  
Keyword(s):  
Nutritional Status ◽  
Energy Homeostasis ◽  
Glucose Transporter ◽  
Glycogen Synthase ◽  
Regulatory Element ◽  
Glycogen Synthesis ◽  
Glycogen Metabolism ◽  
Hepatic Glycogen ◽  
Glycogen Accumulation ◽  
Glucose Transporter 2

Glucagon-like peptide 1 (GLP-1) and PAS kinase (PASK) control glucose and energy homeostasis according to nutritional status. Thus, both glucose availability and GLP-1 lead to hepatic glycogen synthesis or degradation. We used a murine model to discover whether PASK mediates the effect of exendin-4 (GLP-1 analogue) in the adaptation of hepatic glycogen metabolism to nutritional status. The results indicate that both exendin-4 and fasting block the Pask expression, and PASK deficiency disrupts the physiological levels of blood GLP1 and the expression of hepatic GLP1 receptors after fasting. Under a non-fasted state, exendin-4 treatment blocks AKT activation, whereby Glucokinase and Sterol Regulatory Element-Binding Protein-1c (Srebp1c) expressions were inhibited. Furthermore, the expression of certain lipogenic genes was impaired, while increasing Glucose Transporter 2 (GLUT2) and Glycogen Synthase (GYS). Moreover, exendin-4 treatment under fasted conditions avoided Glucose 6-Phosphatase (G6pase) expression, while maintaining high GYS and its activation state. These results lead to an abnormal glycogen accumulation in the liver under fasting, both in PASK-deficient mice and in exendin-4 treated wild-type mice. In short, exendin-4 and PASK both regulate glucose transport and glycogen storage, and some of the exendin-4 effects could therefore be due to the blocking of the Pask expression.

Molecular morphology of hepatic glycogen metabolism

1991 ◽  
Vol 49 ◽  
pp. 48-49
Author(s):  
Robert R. Cardell
Keyword(s):  
Phosphoenolpyruvate Carboxykinase ◽  
Smooth Endoplasmic Reticulum ◽  
Glycogen Synthesis ◽  
Glycogen Metabolism ◽  
Hepatic Glycogen ◽  
Hepatic Gluconeogenesis ◽  
Morphological Aspects ◽  
Molecular Morphology

For over two decades we have studied morphological aspects of hepatic glycogen metabolism, particularly the role of smooth endoplasmic reticulum in this process. Recently investigators have emphasized the role of hepatic gluconeogenesis (formation of glucose from non-carbohydrate precursors) in glycogen synthesis. To contribute new morphological information to this discussion we have developed probes for the detection of the relevant gluconeogenic enzymes by immunocytochemistry and the expression of the genes for the enzymes by in situ hybridization histochemistry. In this report we present: our work on the expression of a gene for the major rate limiting enzyme in hepatic gluconeogenesis, phosphoenolpyruvate carboxykinase (PEPCK).

scholarly journals SERGE, the subcellular site of initial hepatic glycogen deposition in the rat: a radioautographic and cytochemical study.

1985 ◽  
Vol 101 (1) ◽  
pp. 201-206 ◽  
Author(s):  
R R Cardell ◽  
J E Michaels ◽  
J T Hung ◽  
E L Cardell
Keyword(s):  
Smooth Endoplasmic Reticulum ◽  
Periodic Acid ◽  
Glycogen Synthesis ◽  
Hormonal Control ◽  
Hepatic Glycogen ◽  
Cytochemical Study ◽  
Glucose Levels ◽  
Glycogen Deposition ◽  
Glycogen Particles ◽  
Adrenalectomized Rats

Hormonal control of hepatic glycogen and blood glucose levels is one of the major homeostatic mechanisms in mammals: glycogen is synthesized when portal glucose concentration is sufficiently elevated and degraded when glucose levels are low. We have studied initial events of hepatic glycogen synthesis by injecting the synthetic glucocorticoid dexamethasone (DEX) into adrenalectomized rats fasted overnight. Hepatic glycogen levels are very low in adrenalectomized rats, and DEX causes rapid deposition of the complex carbohydrate. Investigation of the process of glycogen deposition was performed by light and electron microscopic (EM) radioautography using [3H]galactose as a glycogen precursor. Rats injected with DEX for 2-3 h and [3H]galactose one hour before being killed displayed an increasing number of intensely labeled hepatocytes. EM radioautography revealed silver grains over small (+/- 1 micron) ovoid or round areas of the cytosome that were rich in smooth endoplasmic reticulum (SER) and contained a high concentration of small dense particles. These distinct areas or foci of SER and presumptive glycogen (SERGE) were most numerous during initial periods of glycogen synthesis. After longer exposure to DEX (4-5 h) more typical deposits of cytoplasmic glycogen were evident in the SERGE regions. Several criteria indicated that the SERGE foci contained glycogen or presumptive glycogen: resemblance of the largest dense particles to beta-glycogen particles in EM; association of 3H-carbohydrate with the foci; removal of particles and label with alpha-amylase; and positive reaction with periodic acid-chromic acid-silver methenamine. The concentration of SER in the small foci and the association of newly formed glycogen particles with elements of SER suggest a role for this organelle in the initial synthesis of glycogen.

Synergistic effects of oPL and insulin on glycogen metabolism in fetal rat hepatocytes

1984 ◽  
Vol 247 (6) ◽  
pp. E714-E718
Author(s):  
M. Freemark ◽  
S. Handwerger
Keyword(s):  
Synergistic Effects ◽  
Fetal Liver ◽  
Glycogen Synthesis ◽  
Rat Hepatocytes ◽  
Glycogen Metabolism ◽  
Placental Lactogen ◽  
Maximum Effect ◽  
Hepatic Glycogen ◽  
Response Curves ◽  
Glucose Incorporation

The interactions between ovine placental lactogen (oPL) and insulin in the regulation of fetal liver glycogen metabolism have been studied in cultured hepatocytes from fetal rats on day 20 of gestation. Both oPL (0.75–22.5 micrograms/ml) and insulin (0.01–1 microM) stimulated dose-dependent increases in [14C]glucose incorporation into glycogen. However, the dose-response curves for the two hormones were not parallel and the maximum effect of oPL was 3.4 times greater than that of insulin (P less than 0.001). The two hormones had synergistic effects on [14C]glucose incorporation at low concentrations and additive effects at maximum concentrations. Ovine growth hormone (oGH) also stimulated [14C]glucose incorporation into glycogen but with a potency only 12.3% that of oPL. Cycloheximide (20 microM) abolished the stimulation of [14C]glucose incorporation by insulin (1 microM), oPL (5 micrograms/ml), and oGH (100 micrograms/ml). Although the glycogenic actions of oPL and insulin may depend on new protein synthesis, the results of these studies suggest that these hormones stimulate glycogen synthesis in fetal liver by different mechanisms. Because the glycogenic actions of oPL are potentiated by insulin, these hormones may act in concert to promote hepatic glycogen storage in the fetus.

The level of the glycogen targetting regulatory subunit R5 of protein phosphatase 1 is decreased in the livers of insulin-dependent diabetic rats and starved rats

2001 ◽  
Vol 360 (2) ◽  
pp. 449-459 ◽  
Author(s):  
Gareth J. BROWNE ◽  
Mirela DELIBEGOVIC ◽  
Stefaan KEPPENS ◽  
Willy STALMANS ◽  
Patricia T. W. COHEN
Keyword(s):  
Phosphatase Activity ◽  
Protein Phosphatase ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Diabetic Rats ◽  
Protein Phosphatase 1 ◽  
Regulatory Subunit ◽  
Hepatic Glycogen ◽  
Insulin Dependent ◽  
Insulin Dependent Diabetic

Hepatic glycogen synthesis is impaired in insulin-dependent diabetic rats owing to defective activation of glycogen synthase by glycogen-bound protein phosphatase 1 (PP1). The identification of three glycogen-targetting subunits in liver, GL, R5/PTG and R6, which form complexes with the catalytic subunit of PP1 (PP1c), raises the question of whether some or all of these PP1c complexes are subject to regulation by insulin. In liver lysates of control rats, R5 and R6 complexes with PP1c were found to contribute significantly (16 and 21% respectively) to the phosphorylase phosphatase activity associated with the glycogen-targetting subunits, GL–PP1c accounting for the remainder (63%). In liver lysates of insulin-dependent diabetic and of starved rats, the phosphorylase phosphatase activities of the R5 and GL complexes with PP1c were shown by specific immunoadsorption assays to be substantially decreased, and the levels of R5 and GL were shown by immunoblotting to be much lower than those in control extracts. The phosphorylase phosphatase activity of R6–PP1c and the concentration of R6 protein were unaffected by these treatments. Insulin administration to diabetic rats restored the levels of R5 and GL and their associated activities. The regulation of R5 protein levels by insulin was shown to correspond to changes in the level of the mRNA, as has been found for GL. The in vitro glycogen synthase phosphatase/phosphorylase phosphatase activity ratio of R5-PP1c was lower than that of GL–PP1c, suggesting that R5–PP1c may function as a hepatic phosphorylase phosphatase, whereas GL–PP1c may be the major hepatic glycogen synthase phosphatase. In hepatic lysates, more than half the R6 was present in the glycogen-free supernatant, suggesting that R6 may have lower affinity for glycogen than R5 and GL

scholarly journals The “Glycogen Granule” Revisited

1994 ◽  
Vol 2 (7) ◽  
pp. 16-18
Author(s):  
Krystyna Rybicka
Keyword(s):  
Electron Microscopy ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Protein Component ◽  
Glycogen Granule ◽  
Regulatory Enzymes ◽  
Ionic Compounds ◽  
Cellular Organelles ◽  
Covalently Bound

There is a gap between biochemical findings and ultrastructural interpretation of “glycogen granules”. Biochemists have recognized that glycogen contains covalently bound proteins. These include enzymes involved in giycogen metabolism: glycogenin (protein primer responsible for initiation of glycogen synthesis), glycogen synthase and phosphorylase, and presumably other regulatory enzymes. The structures formed by the association of glycogen and protein have been called protein-glycogen complexes, considered as proteoglycans, or as dynamic cellular organelles, glycosomes.The question arises as to why the biochemical recognition of a protein component in glycosomes has not been acknowledged in electron microscopy (EM)? This protein is visible in every section stained by uranium (U) and lead (Pb) salts where it appears as 20-30 nm granules (Fig. 1). However, these granules are commonly interpreted as glycogen, despite the fact that glycogen does not react with ionic compounds and therefore cannot be stained by U-Pb.

scholarly journals Defective activation by glucose of hepatic glycogen synthesis in the obese hyperglycaemic mouse

1983 ◽  
Vol 216 (2) ◽  
pp. 491-494 ◽  
Author(s):  
S A Smith ◽  
M A Cawthorne ◽  
A L Levy ◽  
D L Simson
Keyword(s):  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Fold Increase ◽  
Hepatic Glycogen ◽  
Oral Glucose ◽  
Oral Glucose Load ◽  
Glucose Load ◽  
No Activation ◽  
Sustained Activation

The administration of an oral glucose load to 24 h-starved lean (+/?) male C57BL/6 mice produced a rapid, 7-fold increase in the rate of hepatic glycogen synthesis and a sustained activation of glycogen synthase. In contrast, glucose produced only a small (4.5-fold), short-lived increase in hepatic glycogen synthesis in genetically obese (ob/ob) mice and no activation of glycogen synthase.

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