The glucose-induced switch between glycogen phosphorylase and glycogen synthase in the liver is investigated by means of a theoretical approach based on a minimal, bicyclic cascade model involving the reversible phosphorylation of the two enzymes. The aim of the analysis is to evaluate the contribution of different factors to the sequential changes in the activity of glycogen phosphorylase and ...

Sulphate ions have been known for some years to enhance the activity of hepatic glycogen phosphorylase b in vitro. Here we report that intravenous injections of 4.92 mmol of Na2SO4/kg body wt. to rats induced marked hepatic glycogenolysis in vivo, accompanied by polyuria, glycosuria and a mild hyperglycaemia. These effects were observed both in normal (Wistar) rats and in gsd/gsd rats that lack...

In the present study effects of both injections of serotonin and dopamine on haemolymph glucose, total carbohydrates, glycogen and phosphorylase activity in different tissues of intact and eyestalk ablated M.rosenbergii. The haemolymph glucose levels was increased dose dependent in between 10 and 10 mole/prawn after injection of serotonin and dopamine. While the dose 10 mole/prawn induced peak ...

The ability of catecholamines and glucagon to stimulate glycogen phosphorylase activity was examined in hepatocytes isolated from euthyroid and hypothyroid fed female rats. Hypothyroidism did not alter the ability of either phenylephrine or epinephrine to activate glycogen phosphorylase. Activation of glycogen phosphorylase in response to a maximal concentration of isoproterenol, however, was 1...

Rats from the NZR/Mh strain have a genetically-determined deficiency of phosphorylase b kinase activity in the liver which in homozygotes &d/g@ produces a poor activation of glycogen phosphorylase and very high liver glycogen concentrations [I]. They also have low active glycogen synthase activities [l] and previous studies on liver homogenates have shown an inhibition of glycogen synthasephosp...

1,4-Dideoxy-1,4-imino-d-arabinitol (DAB) was identified previously as a potent inhibitor of both the phosphorylated and non-phosphorylated forms of glycogen phosphorylase (EC 2.4.1.1). In the present study, the effects of DAB were investigated in primary cultured rat hepatocytes. The transport of DAB into hepatocytes was dependent on time and DAB concentration. The rate of DAB transport was 192...

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 frac...

Insulin-stimulated glycogen synthase activity in human muscle is reduced in insulin-resistant subjects. Insulin regulation of human muscle glycogen synthase may require activation of a type-1 protein phosphatase (PP-1). We investigated the change of phosphorylase phosphatase and glycogen synthase activities in muscle biopsies obtained during a 2-h hyperinsulinemic euglycemic clamp in 12 insulin...

The development of the phosphorylase-glycogen complex was studied in cells of the myogenic line L6 at different stages of differentiation. Our results indicate that the complex is already present in mononucleated myoblasts. However, several features of the complex observed in the myoblasts, such as the total amount of phosphorylase bound to the polysaccharide, and the type of glycogen agglomera...

Non-metabolized glucose derivatives may cause inactivation of phosphorylase but, unlike glucose, they are unable to elicit activation of glycogen synthase in isolated hepatocytes. We report here that, after the previous inactivation of phosphorylase by one of these glucose derivatives (2-deoxy-2-fluoro-alpha-glucosyl fluoride), glycogen synthase was progressively activated by addition of increa...