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At least 19 recordsLinked to original sources
PubMed1999

Regulation of glycogen synthesis in rat skeletal muscle after glycogen-depleting contractile activity: effects of adrenaline on glycogen synthesis and activation of glycogen synthase and glycogen phosphorylase.

We investigated the effects of insulin and adrenaline on the rate of glycogen synthesis in skeletal muscles after electrical stimulation in vitro. The contractile activity decreased the glycogen concentration by 62%. After contractile activity, the glycogen stores were fully replenished at a constant and high rate for 3 h when 10 m-i.u./ml insulin was present. In the absence of insulin, only 65% of the initial glycogen stores was replenished. Adrenaline decreased insulin-stimulated glycogen synthesis. Surprisingly, adrenaline did not inhibit glycogen synthesis stimulated by glycogen-depleting contractile activity. In agreement with this, the fractional activity of glycogen synthase was high when adrenaline was present after exercise, whereas adrenaline decreased the fractional activity of glycogen synthase to a low level during stimulation with insulin. Furthermore, adrenaline activated glycogen phosphorylase almost completely during stimulation with insulin, whereas a much lower activation of glycogen phosphorylase was observed after contractile activity. Thus adrenaline does not inhibit contraction-stimulated glycogen synthesis.

Animals↗
PubMed1975

Dynamics of liver glycogen: the topochemistry of glycogen synthesis, glycogen content and glycogenolysis under the experimental conditions of glycogen accumulation and depletion.

Using histochemical techniques the glycogen content and the activities of glycogen synthetase (UDPGGT) and phosphorylase were studied in the livers of 106 golden hamsters under following experimental conditions; a) starvation of 16, 36, 48, 72, and 96 hours: b) alloxan-diabetes. Starvation leads to a depletion of liver glycogen during the first 48 hours, which is finally restricted to zone 3 of the liver acinus. After starvation of 72 and 96 hours a new glycogen accumulation is demonstrable in the microvasculatory periphery of the acinus (zone 3 and 2). The process of glycogen depletion is characterized in the beginning by a high phosphorylase activity in all zones of the acinus, later only in the forefield of glycogen content. The weak activity of glycogen synthetase is mainly restricted to zone 3. All phases of glycogen depletion are to be found in alloxan diabetic animals, too. Out of 45 hamsters 23 showed an extreme depletion of glycogen; typical for this situation is a weak or absent glycogen synthetase activity in zone 3 and a broad field of phosphorylase activity in zones 1 and 2. The short stimulation by insulin leads to a considerable increase of glycogen synthetase activity at the portally oriented border of the glycogen area and to a shift of the moderate phosphorylase activity of zone 1. Thus the histochemical characteristics of glycogen depletion are: a shift of the reduced glycogen content in direction of the microvasculatory periphery of the liver acinus (zone 3), caused by a high phosphorylase activity in the portal forefield, while glycogen synthetase activity is low in the glycogen area. The histochemical characteristics of glycogen accumulation are: after a short phase of glycogen synthesis in all hepatocytes a moderate phosphorylase activity in zone 1 leads to a mobilization of the portal glycogen deposits and to an increasing accumulation of glycogen in the peripheral part of the acinus. At the portally oriented border of the glycogen area a high synthetase activity leads to a broadening of the glycogen area in direction of the portal branches. At the end of this process the "normal" pattern of the liver acinus occurs: all hepatocytes are filled with glycogen, the glycogen enzymes are restricted to the periportal border of zone 1.

Animals↗
PubMed1991

Neuroendocrine factors affecting the glycogen metabolism of purified Mytilus edulis glycogen cells: partial characterization of the putative glycogen mobilization hormone--demonstration of a factor that stimulates glycogen synthesis.

A putative glycogen mobilizing hormone (GMH) from the marine mussel Mytilus edulis L. has been partially characterized. GMH activity is present in the cerebral ganglia and the hemolymph serum and promotes the mobilization of glycogen in isolated glycogen cells. The cerebral GMH is trypsin sensitive and partially heat labile and has an apparent molecular mass of greater than 20 kDa. Following fractionation of cerebral extracts by molecular mass, a second factor, with a molecular mass of ca. 1.5 kDa, was discovered. This factor stimulates post-incubation incorporation of 14C into glycogen in isolated glycogen cells.

Animals↗
PubMed2000

Overexpression of protein targeting to glycogen in cultured human muscle cells stimulates glycogen synthesis independent of glycogen and glucose 6-phosphate levels.

There is growing evidence that glycogen targeting subunits of protein phosphatase-1 play a critical role in regulation of glycogen metabolism. In the current study, we have investigated the effects of adenovirus-mediated overexpression of a specific glycogen targeting subunit known as protein targeting to glycogen (PTG) in cultured human muscle cells. PTG was overexpressed both in muscle cells cultured at high glucose (glycogen replete) or in cells incubated for 18 h in the absence of glucose and then incubated in high glucose (glycogen re-synthesizing). In both glycogen replete and glycogen resynthesizing cells, PTG overexpression caused glycogen to be synthesized at a linear rate 1-5 days after viral treatment, while in cells treated with a virus lacking a cDNA insert (control virus), glycogen content reached a plateau at day 1 with no further increase. In the glycogen replete PTG overexpressing cells, glycogen content was 20 times that in controls at day 5. Furthermore, in cells undergoing glycogen resynthesis, PTG overexpression caused a doubling of the initial rate of glycogen synthesis over the first 24 h relative to cells treated with control virus. In both sets of experiments, the effects of PTG on glycogen synthesis were correlated with a 2-3-fold increase in glycogen synthase activity state, with no changes in glycogen phosphorylase activity. The alterations in glycogen synthase activity were not accompanied by changes in the intracellular concentration of glucose 6-phosphate. We conclude that PTG overexpression activates glycogen synthesis in a glucose 6-phosphate-independent manner in human muscle cells while overriding glycogen-mediated inhibition. Our findings suggest that modulation of PTG expression in muscle may be a mechanism for enhancing muscle glucose disposal and improving glucose tolerance in diabetes.

Cells, Cultured↗
PubMed1993

Correlations of glycogen synthase and phosphorylase activities with glycogen concentration in human muscle biopsies. Evidence for a double-feedback mechanism regulating glycogen synthesis and breakdown.

The purpose of this study was to verify in man the relationships of muscle glycogen synthase and phosphorylase activities with glycogen concentration that were reported in animal studies. The upper level of glycogen concentration in muscle is known to be tightly controlled, and glycogen concentration was reported to have an inhibitory effect on synthase activity and a stimulatory effect on phosphorylase activity. Glycogen synthase and phosphorylase activity and glycogen concentration were measured in muscle biopsies in a group of nine normal subjects after stimulating an increase of their muscle glycogen concentration through either an intravenous glucose-insulin infusion to stimulate glycogen synthesis, or an Intralipid (Vitrum, Stockholm, Sweden) infusion in the basal state to inhibit glycogen mobilization by favoring lipid oxidation at the expense of glucose oxidation. Phosphorylase activity increased from 71.3 +/- 21.0 to 152.8 +/- 20.0 nmol/min/mg protein (P < .005) after the glucose-insulin infusion. Phosphorylase activity was positively correlated with glycogen concentration (P = .005 and P = .0001) after the glucose-insulin and Intralipid infusions, respectively. Insulin-stimulated glycogen synthase activity was significantly negatively correlated with glycogen concentration at the end of the Intralipid infusion (P < .005). In conclusion, by demonstrating a negative correlation of glycogen concentration with glycogen synthase and a positive correlation with phosphorylase, this study might confirm in man the double-feedback mechanism by which changes in glycogen concentration regulate glycogen synthase and phosphorylase activities. It suggests that this mechanism might play an important role in the regulation of glucose storage.

Adult↗
PubMed1986

The protein phosphatases involved in cellular regulation. Evidence that dephosphorylation of glycogen phosphorylase and glycogen synthase in the glycogen and microsomal fractions of rat liver are catalysed by the same enzyme: protein phosphatase-1.

Glycogen synthase (labelled in sites-3) and glycogen phosphorylase from rabbit skeletal muscle were used as substrates to investigate the nature of the protein phosphatases that act on these proteins in the glycogen and microsomal fractions of rat liver. Under the assay conditions employed, glycogen synthase phosphatase and phosphorylase phosphatase activities in both subcellular fractions could be inhibited 80-90% by inhibitor-1 or inhibitor-2, and the concentrations required for half-maximal inhibition were similar. Glycogen synthase phosphatase and phosphorylase phosphatase activities coeluted from Sephadex G-100 as broad peaks, stretching from the void volume to an apparent molecular mass of about 50 kDa. Incubation with trypsin decreased the apparent molecular mass of both activities to about 35 kDa, and decreased their I50 for inhibitors-1 and -2 in an identical manner. After tryptic digestion, the I50 values for inhibitors-1 and -2 were very similar to those of the catalytic subunit of protein phosphatase-1 from rabbit skeletal muscle. The glycogen and microsomal fractions of rat liver dephosphorylated the beta-subunit of phosphorylase kinase much faster than the alpha-subunit and dephosphorylation of the beta-subunit was prevented by the same concentrations of inhibitor-1 and inhibitor-2 that were required to inhibit the dephosphorylation of phosphorylase. The same experiments performed with the glycogen plus microsomal fraction from rabbit skeletal muscle revealed that the properties of glycogen synthase phosphatase and phosphorylase phosphatase were very similar to the corresponding activities in the hepatic glycogen fraction, except that the two activities coeluted as sharp peaks near the void volume of Sephadex G-100 (before tryptic digestion). Tryptic digestion of the hepatic glycogen and microsomal fractions increased phosphorylase phosphatase about threefold, but decreased glycogen synthase phosphatase activity. Similar results were obtained with the glycogen plus microsomal fraction from rabbit skeletal muscle or the glycogen-bound form of protein phosphatase-1 purified to homogeneity from the same tissue. Therefore the divergent effects of trypsin on glycogen synthase phosphatase and phosphorylase phosphatase activities are an intrinsic property of protein phosphatase-1. It is concluded that the major protein phosphatase in both the glycogen and microsomal fractions of rat liver is a form of protein phosphatase-1, and that this enzyme accounts for virtually all the glycogen synthase phosphatase and phosphorylase phosphatase activity associated with these subcellular fractions.

Animals↗
PubMed2004

The glycogenic action of protein targeting to glycogen in hepatocytes involves multiple mechanisms including phosphorylase inactivation and glycogen synthase translocation.

Expression of the glycogen-targeting protein PTG promotes glycogen synthase activation and glycogen storage in various cell types. In this study, we tested the contribution of phosphorylase inactivation to the glycogenic action of PTG in hepatocytes by using a selective inhibitor of phosphorylase (CP-91149) that causes dephosphorylation of phosphorylase a and sequential activation of glycogen synthase. Similar to CP-91194, graded expression of PTG caused a concentration-dependent inactivation of phosphorylase and activation of glycogen synthase. The latter was partially counter-acted by the expression of muscle phosphorylase and was not additive with the activation by CP-91149, indicating that it is in part secondary to the inactivation of phosphorylase. PTG expression caused greater stimulation of glycogen synthesis and translocation of glycogen synthase than CP-91149, and the translocation of synthase could not be explained by accumulation of glycogen, supporting an additional role for glycogen synthase translocation in the glycogenic action of PTG. The effects of PTG expression on glycogen synthase and glycogen synthesis were additive with the effects of glucokinase expression, confirming the complementary roles of depletion of phosphorylase a (a negative modulator) and elevated glucose 6-phosphate (a positive modulator) in potentiating the activation of glycogen synthase. PTG expression mimicked the inactivation of phosphorylase caused by high glucose and counteracted the activation caused by glucagon. The latter suggests a possible additional role for PTG on phosphorylase kinase inactivation.

Adenoviridae↗
PubMed1988

The control of glycogen metabolism in yeast. 1. Interconversion in vivo of glycogen synthase and glycogen phosphorylase induced by glucose, a nitrogen source or uncouplers.

The addition of glucose to a suspension of yeast initiated glycogen synthesis and ethanol formation. Other effects of the glucose addition were a transient rise in the concentration of cyclic AMP and a more prolonged increase in the concentration of hexose 6-monophosphate and of fructose 2,6-bisphosphate. The activity of glycogen synthase increased about 4-fold and that of glycogen phosphorylase decreased 3-5-fold. These changes could be reversed by the removal of glucose from the medium and induced again by a new addition of the sugar. These effects of glucose were also obtained with glucose derivatives known to form the corresponding 6-phosphoester. Similar changes in glycogen synthase and glycogen phosphorylase activity were induced by glucose in a thermosensitive mutant deficient in adenylate cyclase (cdc35) when incubated at the permissive temperature of 26 degrees C, but were much more pronounced at the nonpermissive temperature of 35 degrees C. Under the latter condition, glycogen synthase was nearly fully activated and glycogen phosphorylase fully inactivated. Such large effects of glucose were, however, not seen in another adenylate-cyclase-deficient mutant (cyr1), able to incorporate exogenous cyclic AMP. When a nitrogen source or uncouplers were added to the incubation medium after glucose, they had effects on glycogen metabolism and on the activity of glycogen synthase and glycogen phosphorylase which were directly opposite to those of glucose. By contrast, like glucose, these agents also caused, under most experimental conditions, a detectable rise in cyclic AMP concentration and a series of cyclic-AMP-dependent effects such as an activation of phosphofructokinase 2 and of trehalase and an increase in the concentration of fructose 2,6-bisphosphate and in the rate of glycolysis. Under all experimental conditions, the rate of glycolysis was proportional to the concentration of fructose 2,6-bisphosphate. Uncouplers, but not a nitrogen source, also induced an activation of glycogen phosphorylase and an inactivation of glycogen synthase when added to the cdc35 mutant incubated at the restrictive temperature of 35 degrees C without affecting cyclic AMP concentration.

Cyclic AMP↗
PubMed1987

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.

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.

Animals↗
PubMed1975

Glycogen metabolism in white and red muscle or normal and diabetic rats. The glycogen concentration and glycogen synthesis from glucose.

The amount of glycogen and its synthesis from glucose was studied in white muscle (extensor digitorum longus -- EDL) and red muscle (soleus -- SOL) of normal rats and rats with alloxan diabetes by the anthrone method. The amount of glycogen was higher in the white muscle of normal rats, both after a 24 hours' fast (0.37+/-0.02 mg/g as against 0.29+/-0.01 mg/g in the SOL) and with feeding ad libitium (0.72+/-0.05 mg/g as against 0.58+/-0.03 mg/g in the SOL). After a 24 hours' fast, the glycogen content of both muscles was non-significantly higher in alloxan-diabetic rats than in normal animals, whereas in diabetic animals fed ad libitum it was significantly lower than in normal rats fed in the same manner (0.54+/-0.07 mg/g in the EDL and 0.33+/-0.03 mg/g in the SOL). The difference between the glycogen content of the white and red muscle of diabetic rats was also in favour of the white muscle. Muscle glycogenesis from intragastrically administered glucose was higher in the red muscle in all the experimental groups. In normal fed ad libitum the glycogen content of the EDL did not change after glucose administration, but in the SOL it rose from 0.58+/-0.03 to 0.83+/-0.05 mg/g. In fasting (24 hours) normal rats it rose sharply in both muscles, from 0.037+/-0.02 to 0.57+/-0.03 mg/g in the EDL and from 0.29+/-0.01 to 0.87+/-0.06 mg/g in the SOL. In fasting (24 hours) diabetic animals, the glycogen content rose after glucose in the SOL only, from 0.36+/-0.01 to 0.66+/-0.06 mg/g. The differences found in glycogen synthesis in the white and red muscle of normal and diabetic rats are discussed mainly from the aspect of the existence of a relationship between the glycogen concentration and glycogen synthetase activity.

Animals↗
PubMed1992

Schistosoma haematobium: histochemistry of glycogen, glycogen phosphorylase a and glycogen branching enzyme in niridazole-treated females.

The body posterior to the ovary of Schistosoma haematobium females was investigated. Glycogen, glycogen phosphorylase a (EC 2.4.1.1) and glycogen branching enzyme (EC 2.4.1.18) activities were detected in the subtegumental muscle system, parenchyma and mature vitelline cells, whereas no activities were detected in the tegument and immature vitelline cells of the parasite. Administration of a single niridazole dose of 250 mg kg-1 to the pouched mouse (Saccostomus camestris) produced the following changes in S. haematobium females: a relatively rapid depletion of glycogen stores due to disruption of the absorptive surface of the parasite, and to an increase in the activity of glycogen phosphorylase a; a reduction in the phosphorylase a to phosphorylase b-conversion capacity of glycogen phosphorylase phosphatase (EC 3.1.3.17); a decrease in glycogen branching enzyme activity; and a relatively rapid degeneration of parasite cells possibly due to their loss of endogenous energy reserves.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1982

Multisite phosphorylation of glycogen synthase from rabbit skeletal muscle. Phosphorylation of site 5 by glycogen synthase kinase-5 (casein kinase-II) is a prerequisite for phosphorylation of sites 3 by glycogen synthase kinase-3.

Glycogen synthase kinase-5 (casein kinase-II) phosphorylates glycogen synthase on a serine termed site 5. This residue is just C-terminal to the 3 serines phosphorylated by glycogen synthase kinase-3, which are critical for the hormonal regulation of glycogen synthase in vivo. Although phosphorylation of site 5 does not affect the catalytic activity, it is demonstrated that this modification is a prerequisite for phosphorylation by glycogen synthase kinase-3. Since site 5 is almost fully phosphorylated in vivo under all conditions, the role of glycogen synthase kinase-5 would appear to be a novel one in forming the recognition site for another protein kinase.

Animals↗
PubMed1984

Multisite phosphorylation of glycogen synthase. Molecular basis for the substrate specificity of glycogen synthase kinase-3 and casein kinase-II (glycogen synthase kinase-5).

Glycogen synthase kinase-3 was isolated from rabbit skeletal muscle by an improved procedure. The purification was estimated to be 67000-fold and 0.2 mg of enzyme was isolated from 5000 g muscle, corresponding to an overall yield of 7%. The preparation was homogeneous by ultracentrifugal and electrophoretic criteria. The enzyme had a relative molecular mass of 47 kDa by sedimentation equilibrium centrifugation and 51 kDa by SDS-polyacrylamide gel electrophoresis. These values demonstrate that glycogen synthase kinase-3 is monomeric. The Stokes radius of 37 nm suggests the molecule to be asymmetric. The activating factor of the Mg-ATP dependent form of protein phosphatase-1 coeluted with glycogen synthase kinase-3 activity at the final step, establishing that these two activities reside in the same protein. Glycogen synthase kinase-3 phosphorylates glycogen synthase at sites-3, while casein kinase-II phosphorylates site-5, just C-terminal to sites-3 (Picton, C., Aitken, A., Bilham, T. and Cohen, P. (1982) Eur. J. Biochem. 124, 37-45). The basis for the substrate specificities of these protein kinases was investigated using chymotryptic peptides that contain the sites phosphorylated by each enzyme. These studies showed that efficient phosphorylation of sites-3, required the presence of phosphate in site-5 and a region of polypeptide more than 20 residues C-terminal to site-5. In contrast, efficient phosphorylation by casein kinase-II does not require this C-terminal region, and the results are consistent with the view that the enzyme recognises acidic residues immediately C-terminal to site-5.

Amino Acid Sequence↗
PubMed1988

The control of glycogen metabolism in yeast. 2. A kinetic study of the two forms of glycogen synthase and of glycogen phosphorylase and an investigation of their interconversion in a cell-free extract.

Two interconvertible forms of glycogen synthase and glycogen phosphorylase, one active (a) or the other less active (b), were predominantly present in a thermosensitive adenylate-cyclase-deficient mutant that had been preincubated at the restrictive temperature of 35 degrees C, either in the presence or in the absence of glucose. Glycogen phosphorylase was at least 20-fold less active after incubation of the cells in the presence of glucose, but this residual activity had kinetic properties identical to those of the active form of enzyme, obtained after incubation in the absence of glucose; this suggests that the b form might be completely inactive and that the low activity measured after glucose treatment must be attributed to a residual amount of phosphorylase a. By contrast, the kinetic properties of the two forms of glycogen synthase were very different. When measured in the absence of glucose 6-phosphate, the two forms of enzyme had a similar affinity for UDP-Glc but differed essentially by their Vmax. Glucose 6-phosphate had no effect on synthase a, but increased both Vmax and Km of synthase b; these effects, however, were in great part counteracted by sulfate and by inorganic phosphate, the latter also having the property of increasing the Km of the a form, without affecting Vmax. It was estimated that at physiological concentrations of substrates and effectors, synthase a was about 20-fold more active than synthase b. When an extract of cells that had been preincubated in the absence of glucose was gel-filtered and then incubated at 30 degrees C, phosphorylase was progressively fully inactivated and synthase was partially activated; these reactions were severalfold faster and, in the case of glycogen synthase, more complete in the presence of 10 mM glucose 6-phosphate. When a gel-filtered extract of cells that had been preincubated in the presence of glucose was incubated at 30 degrees C in the presence of ATP-Mg and EGTA, phosphorylase became activated and synthase was inactivated; the first of these two reactions was severalfold stimulated by micromolar concentrations of Ca2+, whereas both reactions were completely inhibited by 10 mM glucose 6-phosphate and only slightly and irregularly stimulated by cyclic AMP.

Adenosine Triphosphate↗
PubMed1990

Insulin and the stimulation of glycogen synthesis. The road from glycogen structure to glycogen synthase to cyclic AMP-dependent protein kinase to insulin mediators.

The enhanced phosphorylations via cAMP, Ca2+ mobilization, and diacyl glycerol formation via the activation of the respective kinases is now classical. The decreased phosphorylation via inhibition of adenylate cyclase via the alpha adrenergic receptor is also becoming understood. What the insulin studies on the control of glycogen synthesis have taught us is that the rate limiting enzyme glycogen synthase is regulated by multiple covalent phosphorylation in an elegant but complex manner. The overall pattern of dephosphorylation is influenced by effecting both phosphatase and kinase activities in a set of interrelated mechanisms. In the presence of glucose, in muscle, fat, and liver under physiological conditions G-6-P acts as a signal to stimulate the phosphatase. An additional stimulation could occur via a novel insulin phosphatase stimulatory mediator. The phosphatase is also stimulated by at least three covalent mechanisms involving altered phosphorylation state. In one there is a decreased phosphorylation of the phosphatase inhibitor 1 potentially related to decreased cAMP-dependent protein kinase activity. In the second, there is decreased phosphorylation of the deinhibitor also potentially related to decreased cAMP-dependent protein kinase phosphorylation. In the third, an increased activity of casein kinase 2 could activate the ATP-Mg dependent phosphatase by an increased phosphorylation of phosphatase inhibitor 2 (modulatory subunit). In the liver, allosteric control of the phosphatase by G-6-P and nucleotides is of great importance. Insulin also stimulates the phosphatase in long-term experiments via increased protein synthesis. It is clear that future work will be required to determine which species of the various classes of phosphatases are regulated in short-term and long-term regulation by insulin. In terms of kinases, the effects of insulin to inactivate and desensitize the cAMP-dependent protein kinase are established. The molecular mechanisms of this effect remain to be worked out. The enhanced activity of MAP and S-6 kinase would appear to be part of a cascade of reactions perhaps originating in the autophosphorylation and activation of the insulin receptor tyrosine kinase. The mechanism of the short-term activation of casein kinase 2 remains to be elucidated. A cAMP-dependent protein kinase inhibitory mediator, which also inhibits adenylate cyclase is an important element in the regulation of kinase and adenylate cyclase activity by insulin. Its physiological significance must be established in the future, in terms of its control of glycogen synthase activation by insulin. Clearly this kinase inhibitor as well as the phosphatase stimulator are potential regulators of glycogen synthase activity by insulin.

Amino Acid Sequence↗
PubMed1975

Studies on glycogen metabolism in human leukemic cells. I. Glycogen content, glycogen synthetase forms and their metabolic interconversion.

A decrease in glycogen content and glycogen-synthetase activity was observed in leukemic leucocytes compared to those of normal humans, but the decrease was lesser in chronic myeloid leukemic leucocytes than in those of acute leukemic patients. Incubation of crude leucocyte homogenates at 30 degrees C before assay of the enzyme activity, revealed a conversion of the glycogen-synthetase from the D to the I form. It took place if the enzyme source were enzyme extracts from acute myeloblastic, acute lymphoblastic, chronic lymphocytic, acute menoblastic and undifferenciate leucocytes. The conversion did not occur in crude homogenates from leucocytes of chronic myeloid leukemic patients. ATP-Mg caused a conversion of the glycogen-synthetase I form to the D form in acute myeloblastic, chronic lymphocytic and undifferenciate leukemic leucocytes. This conversion was not observed in chronic myelocytic leukemic leucocytes.

Glycogen↗