Glycogen phosphorylase

About: Glycogen phosphorylase is a(n) research topic. Over the lifetime, 6589 publication(s) have been published within this topic receiving 209856 citation(s).

Glycogen Synthase Kinase-3 from Rabbit Skeletal Muscle

Abstract: Publisher Summary This chapter discusses glycogen synthase kinase-3 from rabbit skeletal muscle. Glycogen synthase kinase-3 is one of the five glycogen synthase kinases that are identified in skeletal muscle, and is of major importance in determining the kinetic properties of glycogen synthase in vivo. It catalyzes the phosphorylation of three serine residues on glycogen synthase, converting the enzyme from a form that is almost fully active in the absence of glucose-6P, to one that is largely dependent on this allosteric activator. Glycogen synthase kinase-3 also has a second activity that is not shared by any other protein kinase—namely, the ability to activate an enzyme termed the MgATP-dependent protein phosphatase. Glycogen synthase may also contain traces of a modified form of phosphorylase kinase that has lost its sensitivity to regulation by calcium ions, and is therefore, no longer inhibited by ethylene glycol tetraacetic acid (EGTA). This is largely removed by passing glycogen synthase through phosphocellulose.

A comparison of three methods of glycogen measurement in tissues.

Abstract: Three methods have been used for analysis of glycogen in tissue homogenates: hydrolysis of the tissue in acid and followed by enzymic analysis of the resulting glucose; enzymic hydrolysis with amylo-α-1,4-α-1,6-glucosidase, again followed by enzymic measurement of glucose; and degradation of the glycogen with phosphorylase and debrancher complex coupled to measurement of the resulting glucose-1- P . The two enzymic procedures yielded equivalent results with all tissues examined (brain, liver, muscle and polymorphonuclear leucocytes). Acid hydrolysis of the tissues resulted in higher values for brain tissue only, presumably due to the hydrolysis of the gangliosides and cerebrosides present in brain.

Eicosonoid metabolism and beta-adrenergic mechanisms in coronary arterial smooth muscle: potential compartmentation of cAMP

Abstract: Beta-Adrenergic relaxation in bovine coronary arteries is enhanced by inhibition of eicosonoid metabolism and inhibited by its stimulation. We investigated the interaction between eicosonoid metabolism and beta-adrenergic mechanisms by studying the effect of perturbations of eicosonoid metabolism on vascular adenosine 3',5'-monophosphate (cAMP) content and the cAMP-dependent relaxation of isometric force and activation of glycogen phosphorylase. KCl (35 mM) elicited a contraction, activated phosphorylase, and slightly decreased cAMP content. Isoproterenol (10(-7) M) relaxed the KCl contraction, further increased phosphorylase activity, and increased cAMP. Neither indomethacin (5 X 10(-6) M) nor arachidonic acid (3 X 10(-5) M) affected the KCl contraction, but arachidonic acid increased both cAMP and phosphorylase activity and indomethacin decreased cAMP. Indomethacin potentiated the relaxation induced by isoproterenol but inhibited the activation of phosphorylase and had no effect on the isoproterenol-induced increase in cAMP. Arachidonic acid, on the other hand, inhibited the isoproterenol-induced relaxation but potentiated both the increases of phosphorylase activity and cAMP. Thus neither relaxation nor phosphorylase activity was related in a straightforward manner to the total cAMP content. A direct relation between cAMP, relaxation, and phosphorylase can be reconciled with the antiparallel effects of alterations of eicosonoid metabolism observed in this study by a proposed model in which the effects of cAMP are assumed to be functionally compartmentalized.