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PubMed1989

The substrate and sequence specificity of the AMP-activated protein kinase. Phosphorylation of glycogen synthase and phosphorylase kinase.

In addition to acetyl-CoA carboxylase and HMG-CoA reductase, the AMP-activated protein kinase phosphorylates glycogen synthase, phosphorylase kinase, hormone-sensitive lipase and casein. A number of other substrates for the cyclic AMP-dependent protein kinase, e.g., L-pyruvate kinase and 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase, are not phosphorylated at significant rates. Examination of the sites phosphorylated on acetyl-CoA carboxylase, hormone-sensitive lipase, glycogen synthase and phosphorylase kinase suggests a consensus recognition sequence in which the serine residue phosphorylated by the AMP-activated protein kinase has a hydrophobic residue on the N-terminal side (i.e., at -1) and at least one arginine residue at -2, -3 or -4. Substrates for cyclic AMP-dependent protein kinase which lack the hydrophobic residue at -1 are not substrates for the AMP-activated protein kinase.

Acetyl-CoA Carboxylase↗
PubMed1990

Phosphorylase phosphatase activities of rat liver in streptozotocin-diabetes.

Protein phosphatase-1 and 2A, accounting for all the hepatic activity regulating phosphorylase, were assayed in streptozotocin-induced (8 weeks) diabetic Wistar rats. Cytosolic protein phosphatase-1 and 2A were distinguished by chromatography on heparin-Sepharose and by inhibition with inhibitor-2. Approx. 25-35% increases in type-1 phosphorylase phosphatase activity measured in cytosols were registered in diabetic rats when compared with control and 24 h fasting animals. The enrichment of protein phosphatase-1 in the cytosol of streptozotocin-treated rat livers could not be attributed to the reduced glycogen content with the onset of diabetes, since this elevated level of type-1 phosphatase was not observed in fasting rats with low glycogen content. The translocation of type-1 phosphatase from the particulate fraction into the cytosol was also recorded in trypsin-treated samples of diabetic rat livers. The apparent molecular weight of type-1 phosphatase in the cytosol of control and fasted rats was 160,000 as judged by gel filtration. The type-1 phosphatase activity that was released from the particulate fraction by streptozotocin-induced diabetes identified a further enzyme species (Mr 110,000) in the cytosol. Our data imply that the higher levels of cytosolic protein phosphatase-1 in diabetic rat liver could be a consequence of the dissociation of the catalytic subunit of protein phosphatase-1 and the glycogen-binding subunit in rat livers.

Animals↗
PubMed1995

Dose-dependent elevation of cyclic AMP, activation of glycogen phosphorylase, and release of lactate by amylin in rat skeletal muscle.

We report here our investigation of the role of cyclic AMP (cAMP) in amylin signal transduction in isolated strips of soleus muscle. Rat amylin, at 100 nM, increased cAMP levels, from 0.431 +/- 0.047 to a peak of 1.24 +/- 0.01 pmol cAMP/mg wet wt. after 5 min, in the absence of added phosphodiesterase inhibitor. The EC50 of the response was 0.48 nM (+/- 0.12 log units) in the absence of insulin and 0.3 nM (+/- 0.18 log units) in the presence of 7.1 nM insulin. The response seen with a maximally effective concentration of amylin (10 nM) was similar to that seen with a maximally effective concentration of epinephrine (1 microM) under the same conditions. Consistent with the observed rise in cAMP there was an increase in glycogen phosphorylase a (EC50 2.2 nM +/- 0.25 log units), decreased glycogen content (EC50 0.9 nM +/- 0.22 log units) and enhanced production of lactate (EC50 1.5 nM +/- 0.33 log units). These data support the concept that amylin promotes glycogenolysis in skeletal muscle and enhances production of lactate through glycolysis as a result of activation of Gs coupled receptors, stimulation of adenylate cyclase, elevation of cAMP levels and activation of glycogen phosphorylase.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Human astrocytoma U251 RNA and genomic brain glycogen phosphorylase sequences.

There are two versions of human brain glycogen phosphorylase (B-GP) cDNA in the literature that differ significantly in their C-terminal coding and 3' untranslated regions; one isolated from human fetal brain, and the other from human brain astrocytoma cell line U251. A 280 bp absence in the cDNA sequence isolated from human brain astrocytoma cell line U251 changes the predicted protein length from 842 aa (estimated from fetal brain cDNA) to 862 aa. RNA and genomic DNA were isolated from U251 cells and the 280 bp region of interest was amplified by the polymerase chain reaction (PCR). Sequence analysis of the amplified region has unexpectedly confirmed the presence of the 280 bp in U251 RNA and genomic DNA. Thus, the predicted protein length of 842 aa, as reported for fetal brain glycogen phosphorylase, is most likely the correct one.

Astrocytoma↗
PubMed1989

T-lymphocyte dysfunction in the elderly associated with zinc deficiency and subnormal nucleoside phosphorylase activity: effect of zinc supplementation.

The present study was conducted in an attempt to explore a possible mechanism for zinc-deficiency-induced T-lymphocyte dysfunction in the elderly. Eight elderly subjects aged 65-78 years served in this study. All subjects were anergic, zinc-deficient and had low activity of erythrocyte nucleoside phosphorylase. Baseline values for zinc status and immunological indices were established after which subject were treated with zinc acetate (60 mg elemental zinc per day given orally) for a period of 4 1/2 months. Zinc supplementation resulted in a significant increase in the concentrations of zinc in plasma (P less than 0.001), erythrocytes (P less than 0.05), lymphocytes (P less than 0.001) and neutrophils (P less than 0.005). The activity of nucleoside phosphorylase in erythrocytes increased significantly (P less than 0.001) as a result of zinc treatment. This was associated with significant improvement in the delayed cutaneous hypersensitivity reactions.

Acetates↗
PubMed1991

Interaction of flavin mononucleotide with dimeric and tetrameric forms of muscle phosphorylase beta.

Interaction of flavin mononucleotide (FMN) with dimeric and tetrameric forms of rabbit muscle glycogen phosphorylase beta has been studied under the conditions when allosteric activator binding sites are saturated by AMP (1 mM AMP; pH 6.8; 17 degrees C). Simultaneous use of schlieren optical system and photoelectric scanning absorption optical system of analytical ultracentrifuge Spinco, model E, makes it possible to register the oligomeric state of the enzyme and calculate the degree of saturation of individual oligomeric enzyme forms by FMN. The apparent association constant for the equilibrium dimer in equilibrium with tetramer decreased with increasing FMN concentration. The microscopic dissociation constants for the complexes of dimeric and tetrameric forms of glycogen phosphorylase beta with FMN have been found to be equal to 10 and 79 microM, respectively.

Adenosine Monophosphate↗
PubMed1986

Effects of streptozotocin-diabetes, fasting and adrenaline on phosphorylase phosphatase activities of rat skeletal muscle.

The distribution of the spontaneous and trypsin-stimulated phosphorylase phosphatase activities between glycogen particles and cytosol was examined in muscle extracts obtained from rats that had been fasted, made diabetic with streptozotocin or injected with adrenaline. In all conditions the particle-bound phosphatase activities decreased, glycogen was degraded and phosphorylase was released from the particles into the cytosol. However, in fasting and diabetes (but not after adrenaline) the combined glycogen particle + cytosolic phosphatase activities decreased, indicating that the activity lost from the particles was not simply shifted to the cytosol. Fasting and diabetes (but not adrenaline) also decreased the phosphatase-activating ability of the muscle extracts, which was, at least in part, attributable to the protein kinase FA. These data indicate the presence of at least two different mechanisms affecting the phosphatase system, one modified by fasting and diabetes, the other by adrenaline.

Animals↗
PubMed1985

Altered membrane association of glycogen phosphorylase in the dystrophic chicken.

The subcellular distribution of glycogen phosphorylase in pectoralis muscle from normal and dystrophic chickens was determined as a function of age. A substantially larger proportion of the total activity was associated with membranous cellular organelles, both mitochondria and sarcoplasmic reticulum, in preparations from dystrophic birds. The difference could be detected as early as 2 weeks ex ovo. Interaction of phosphorylase with cellular membranes may provide a probe for the underlying membrane defect in this dystrophy model.

Age Factors↗
PubMed1985

Phosphorolytic and ribosyl transfer mechanisms of purified chicken liver purine nucleoside phosphorylase.

Purified chicken liver purine nucleoside phosphorylase shows two ionizable groups at the active site whose pKa were near pH 6.9 and 8; the molecular weight (67,000-89,000) depends on the protein concentration. Initial velocity studies and product inhibition patterns were consistent with a random mechanism, which is rapid equilibrium in the phosphorolytic reaction with a dead-end complex, but not in the synthetic reaction. Free inorganic orthophosphate purine nucleoside phosphorylase (Sephadex G-100) catalyzes a pentosyl transfer reaction from inosine to guanine according to a random Bi, Bi mechanism.

Animals↗
PubMed1987

Chicken liver purine nucleoside phosphorylase activity dependency of the redox state of sulfhydryl groups.

1. Double reciprocal plots (1/v vs 1/S) for nucleoside substrates of chicken liver purine nucleoside phosphorylase were non linear at high inosine or deoxyinosine concentrations (greater than 0.1 mM). The appearance of downward curvatures may be correlated with the oxidation of sulfhydryl groups of the enzyme. 2. 5,5'-Dithiobis-(2-nitrobenzoic acid) reacts with four sulfhydryl groups in the native enzyme, but upon denaturation with sodium dodecylsulfate six sulfhydryl groups react with this reagent. 3. Inosine, ribose-1-phosphate, hypoxanthine and orthophosphate partially protect sulfhydryl groups from the reaction with Ellman's reagent. 4. Inhibition of purine nucleoside phosphorylase by p-chloromercuribenzoate and 5,5'-dithiobis-(2-nitrobenzoic acid) follows a second order reaction kinetics.

Animals↗
PubMed1987

Effect of dietary protein on purine nucleoside phosphorylase and xanthine dehydrogenase activities of liver and kidney in chicken and pigeon.

Comparative studies were made on the effects of diets of different protein contents on the activities of purine nucleoside phosphorylase and xanthine dehydrogenase of avian livers and kidneys. In chicken liver and kidney, both enzyme activities were increased with high protein diet, confirming the previous results. In pigeon liver, only purine nucleoside phosphorylase was increased but xanthine dehydrogenase activity was not detected after feeding a high protein diet, while both enzyme activities were increased in the pigeon kidney. The increase in the levels of plasma oxypurines in pigeon serum was consistent with the result that the xanthine dehydrogenase activity of pigeon was not detected in the liver but in the kidney.

Animals↗
PubMed1988

Purine nucleoside phosphorylase heterogeneity in the mouse as analyzed by isoelectric focusing and specific activity.

1. Isoelectric focusing in polyacrylamide gels identified three erythrocytic electrophoretic patterns of purine nucleoside phosphorylase in a survey of 16 mouse strains. 2. Three strain-specific electrophoretic types were also evident in liver, kidney and spleen leukocytes. 3. There are 3-fold differences in purine nucleoside phosphorylase activities between strains for several tissues; C57BL/6J and Mus spretus having the greatest and the least activity, respectively. 4. Within strains there were up to 8-fold tissue-specific differences in activity with the order from greatest to least being: liver, kidney, spleen leukocyte, erythrocyte, heart.

Animals↗
PubMed1990

Kinetic characterization of glycogen phosphorylase B from skeletal muscle of the mullet Liza ramada.

1. Glycogen phosphorylase purified from muscle of mullet (Liza ramada) has been kinetically characterized. 2. Kinetic analysis for the substrates glucose-1-P and glycogen showed no homotropic co-operativity. AMP exhibited only a slight homotropic co-operative behaviour, although it caused a decrease in the Km for glucose-1-P. 3. Glucose, ATP and glucose-6-P behaved as phosphorylase b inhibitors. Kinetic analysis of the inhibition showed the characteristic heterotropic effect both for the substrate glucose-1-P and the activator AMP. 4. However, glucose-6-P, which enhances the co-operativity between AMP molecules, lost its heterotropic effect on the glucose-1-P saturation curve.

Adenosine Monophosphate↗
PubMed1983

Changes in hemolymph glucose, hepatopancreas glycogen, total carbohydrates, phosphorylase and amino transferases of sumithion-stressed freshwater rice-field crab (Oziotelphusa senex senex).

Adult crabs were exposed to 3 concentrations of sumithion with a control group over a 20-day period. Hemolymph glucose levels were monitored in each group over the course of the experiment. The group demonstrating the most acute and sustained hyperglycemia (2 ppm sumithion) was then analyzed, as also the controls for changes in hepatopancreas glycogen, total carbohydrates, phosphorylase and aminotransferases. Significant (P less than 0.001) depressions in hepatopancreas glycogen and total carbohydrates and elevations of phosphorylase and transaminases were observed in sumithion-stressed crabs when compared with controls. These changes are discussed with respect to gluconeogenesis and possible influences of hyperglycemic hormone, which is released into hemolymph of stressed crab.

Animals↗
PubMed1992

Histamine activates phosphorylase and inositol phosphate production in guinea pig hepatocytes.

In guinea pig hepatocytes, histamine increased phosphorylase activity and inositol phosphate production. Similar effects were obtained with 2-(2-aminoethyl)-thiazole, a histamine H1 receptor agonist, but not with dimaprit or impromidine, H2 receptor agonists. These effects of histamine were dose-dependently inhibited by the H1 antihistamines, (+)-chlorpheniramine and mepyramine (pyrilamine) but not by cimetidine or ranitidine, H2 antagonists. (+)-Chlorpheniramine and mepyramine had similar potencies (apparent Ki values approximately 3 nM) when incubated with the cells for 1 min (phosphorylase a assays) but the former was 15-20-fold more potent than the latter at longer incubation times (apparent Ki values approximately 3-4 nM and 45-90 nM, respectively) indicating that mepyramine is actively metabolized by guinea pig hepatocytes. Histamine increased cytosol calcium approximately 2-fold, an effect also mediated through H1 receptors. The actions of histamine were not affected by in vivo ADP-ribosylation by pertussis toxin. Our data clearly indicate that histamine modulates the metabolism of guinea pig hepatocytes via activation of H1 receptors. These receptors are coupled to the phosphoinositide turnover-calcium mobilization signalling pathway through a pertussis toxin-insensitive process.

Animals↗
PubMed2005

Inhibition of thymidine phosphorylase (PD-ECGF) from SD-lymphoma by phosphonomethoxyalkyl thymines.

A series of thymine phosphonomethoxyalkyl derivatives were evaluated for their ability to inhibit thymidine phosphorylase (dThdPase) purified from rat spontaneous T-cell lymphoma. A kinetic study of thymidine phosphorolysis catalyzed by dThdPase was performed with thymidine and/or inorganic phosphate as substrates. Data show that the substantial inhibitory effect of these acyclic nucleotide analogues is decreasing in the order of (R)-FPMPT>(S)-FPMPT>or=(R)-HPMPT>(S)-PMPT>(S)-HPMPT>PMET>or=(R)-PMPT. The inhibitory potency (K(i)/(dThd)K(m)) of the most efficient inhibitors from this series against T-cell lymphoma enzyme is 0.0026 for (R)-FPMPT and 0.0048 for (S)-FPMPT. The studied compounds do not inhibit Escherichia coli and human enzyme and possess lower inhibitory potency against rat liver thymidine phosphorylase.

Animals↗
PubMed2003

A new class of glycogen phosphorylase inhibitors.

A new class of diacid analogues that binds at the AMP site not only are very potent but have approximately 10-fold selectivity in liver versus muscle glycogen phosphorylase (GP) in the in vitro assay. The synthesis, structure, and in vitro and in vivo biological evaluation of these liver selective glycogen phosphorylase inhibitors are discussed.

Adenosine Triphosphate↗
PubMed2005

Stopped-flow studies of guanine binding by calf spleen purine nucleoside phosphorylase.

The binding of guanine to calf spleen purine nucleoside phosphorylase at 20 degrees C, in 20 mM Hepes-NaOH buffer, pH 7.0, at several ionic strength between 5 and 150 mM was investigated using a stopped-flow spectrofluorimeter. The kinetic transients registered after mixing a protein solution with ligand solutions of different concentrations were simultaneously fitted by several association reaction models using nonlinear least-squares procedure based on numerical integration of the chemical kinetic equations appropriate for given model. It is concluded that binding of a guanine molecule by each of the binding sites is a two-step process and that symmetrical trimeric calf spleen purine nucleoside phosphorylase represents a system of (identical) interacting binding sites. The interaction is visible through relations between the rate constants and non-additivity of changes in "molar" fluorescence for different forms of PNP-guanine complexes. It is also probable that electrostatic effects in guanine binding are weak, which indicates that it is the neutral form of the ligand which is bound and dissociated by PNP molecule.

Animals↗