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, G(L), 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 sub...

The form of protein phosphatase-1 associated with hepatic glycogen (PP1G) was purified to near homogeneity from rat liver by affinity chromatography on microcystin-Sepharose and gel-filtration. The enzyme is a heterodimer consisting of the catalytic subunit of PP1 (the alpha and beta isoforms) complexed to a 33 kDa glycogen-binding (GL) subunit. The GL subunit binds phosphorylase a with high af...

Epinephrine and the a-adrenergic agonist phenylephrine activated phosphorylase, glycogenolysis, and gluconeogenesis from lactate in a dose-dependent manner in isolated rat liver parenchymal cells. The half-maximally active dose of epinephrine was lo-’ M and of phenylephrine was 10m6 M. These effects were blocked by a-adrenergic antagonists including phenoxybenzamine, but were largely unaffected...

Stimulation of skeletal muscle to contract activates phosphorylase b-to-a conversion and glycogenolysis. Despite reversal of the increase in percentage of phosphorylase a after a few minutes, continued glycogen breakdown can occur during strenuous exercise. Hypoxia causes sustained glycogenolysis in skeletal muscle without an increase in percentage of phosphorylase a. We used this model to obta...

OBJECTIVE To determine whether transient ST-T alterations in patients with unstable angina are associated with an increase in plasma glycogen phosphorylase BB concentrations on admission to hospital. DESIGN Prospective screening of patients with unstable angina for markers of myocardial cell damage. SETTING Accident and emergency department of university hospital. PATIENTS 48 consecutive ...

AMP-activated protein kinase (AMPK) is proposed to stimulate fat and carbohydrate catabolism to maintain cellular energy status. Recent studies demonstrate that pharmacologic activation of AMPK and mutations in the enzyme are associated with elevated muscle glycogen content in vivo. Our purpose was to determine the mechanism for increased muscle glycogen associated with AMPK activity in vivo. A...

The next step in the purification involved degradation of the glycogen in the proteinglycogen complex, in order to solubilize the various enzyme activities. This was achieved for glycogen synthase by incubation of the complex with 0.5~-potassium phosphate and 5 mM-AMP, which activates the endogenous phosphorylase that is present in the complex (Nimmo et al., 1976), followed by extensive dialysi...

It is well known that an alteration in insulin activation of skeletal muscle glycogen synthase is associated with insulin resistance. To determine whether this defect in insulin action is specific to skeletal muscle, or also present in liver, simultaneous biopsies of these tissues were obtained before and during a euglycemic hyperinsulinemic clamp in spontaneously obese insulin-resistant male r...

Glycogen phosphorylase inhibitors are considered as potential antidiabetic agents. 3-(β-d-Glucopyranosyl)-5-substituted-1,2,4-triazoles were prepared by acylation of O-perbenzoylated N (1)-tosyl-C-β-d-glucopyranosyl formamidrazone and subsequent removal of the protecting groups. The best inhibitor was 3-(β-d-glucopyranosyl)-5-(2-naphthyl)-1,2,4-triazole (K i = 0.41 μM against rabbit muscle glyc...

Under normal conditions glycogen cannot be detected in adipose tissue. When animals are first starved and then fed on a carbohydrate diet, glycogen appears temporarily in this tissue (see Hausberger & Neuenschwander-Lemmer, 1939). Tuerkischer & Wertheimer (1942) investigated the phenomenon in detail and found that, in the rat, this deposition of glycogen was particularly marked in the brown adi...