Incorporation and release of the radioactivity in the liver glycogen of 18.5- and 19.5-day-old rat foetuses were studied after intravenous injection of E11-14C]glycerol. Incorporation occurred during 1 h after injection of the radioactive tracer to the foetus; then, the incorporated radioactivity decreased. Glycogen content in the liver, and glycogen phosphorylase and glycogen synthase were not...

Interventions such as glycogen depletion, which limit myocardial anaerobic glycolysis and the associated proton production, can reduce myocardial ischemic injury; thus it follows that inhibition of glycogenolysis should also be cardioprotective. Therefore, we examined whether the novel glycogen phosphorylase inhibitor 5-Chloro-N-[(1S,2R)-3-[(3R,4S)-3,4-dihydroxy-1-pyrrolidinyl)]-2-hydroxy-3-oxo...

The Ca”-stimulated phosphorylation of rabbit muscle glycogen synthase (EC 2.4.1.11) catalyzed by phosphorylase kinase (EC 2.7.1.38) was characterized and compared with the reaction involving phosphorylase (EC 2.4.1.1). By comparing reaction rates at equal concentrations (on a mass basis), the activity ratio of phosphorylase/synthase varied from 30 (0.05 mg/ml) to approximately 8 (1 mg/ml). A ba...

High glucose concentration suppresses hepatic glycogenolysis by allosteric inhibition and dephosphorylation (inactivation) of phosphorylase-a. The latter effect is attributed to a direct effect of glucose on the conformation of phosphorylase-a. Although glucose-6-phosphate (G6P), like glucose, stimulates dephosphorylation of phosphorylase-a by phosphorylase phosphatase, its physiological role i...

The effects of hypothyroidism on glycogen metabolism in rat skeletal muscle were studied using the perfused rat hindlimb preparation. Three weeks after propylthiouracil treatment, serum thyroxine was undetectable and muscle glycogen and Glc-6-P were decreased. Basal and epinephrine-stimulated phosphorylase a and phosphorylase b kinase activities were also significantly reduced, as were epinephr...

The animal glycogen molecule has to be designed in accordance with its metabolic function as a very effective fuel store allowing quick release of large amounts of glucose. In addition, the design should account for a high capacity of glucose storage in the least possible space. We have studied the optimization of these variables by means of a mathematical model of the glycogen molecule. Our re...

It has long been known that muscle phosphorylase b has a strict requirement for adenylic acid (5’-AMP) (1). Phosphorylase a, on the other hand, is active without 5’-AMP (2) and although 5’-AMP may increase velocity somewhat, the increase according to most reports is not more than 50%. In connection with the use of phosphorylase and glycogen to measure low levels of inorganic orthophosphate, it ...

The kinetic properties of a glutaraldehyde-modified phosphorylase b have been examined to understand further the mechanism of allosteric transition of this enzyme. The sigmoidal response to AMP, which is observed with native glycogen phosphorylase b, cannot be demonstrated with the modified enzyme. This enzyme derivative also exhibits no homotropic cooperativity of glucose 1 -phosphate under co...