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At least 595 records · Page 33Linked to original sources
PubMed1985

[Regulatory properties of phosphorylase from chicken skeletal muscle].

The main kinetic parameters for purified phosphorylase kinase from chicken skeletal muscle were determined at pH 8.2: Vm = 18 micromol/min/mg; apparent Km values for ATP and phosphorylase b from rabbit muscle were 0.20 and 0.02 mM, respectively. The activity ratio at pH 6.8/8.2 was 0.1-0.4 for different preparations of phosphorylase kinase. Similar to the rabbit enzyme, chicken phosphorylase kinase had an absolute requirement for Ca2+ as demonstrated by complete inhibition in the presence of EGTA. Half-maximal activation occurred at [Ca2+] = 0.4 microM at pH 7.0. In the presence of Ca2+, the chicken enzyme from white and red muscles was activated 2-4-fold by saturating concentrations of calmodulin and troponin C. The C0.5 value for calmodulin and troponin C at pH 6.8 was 2 and 100 nM, respectively. Similar to rabbit phosphorylase kinase, the chicken enzyme was stimulated about 3-6-fold by glycogen at pH 6.8 and 8.2 with half-maximal stimulation occurring at about 0.15% glycogen. Protamine caused 60% inhibition of chicken phosphorylase kinase at 0.8 mg/ml. ADP (3 mM) at 0.05 mM ATP caused 85% inhibition with Ki = 0.2 mM. Unlike rabbit phosphorylase kinase, no phosphorylation of the chicken enzyme occurred in the presence of the catalytic subunit of cAMP-dependent protein kinase. Incubation with trypsin caused 2-fold activation of the chicken enzyme.

Adenosine Diphosphate↗
PubMed1981

Liver glycogenosis caused by a defective phosphorylase system: hemolysate analysis.

Investigated were 24 cases of glycogenosis caused by a reduction in liver phosphorylase activity. The intravenous glucagon tolerance test could not discriminate between phosphorylase kinase deficiency [glycogen storage disease (GSD) IX] and phosphorylase deficiency (GSD VI). These two subgroups were distinguished by hemolysate enzyme assays: (1) GSD IX was characterized by a residual phosphorylase kinase activity, a low activation curve for endogenous phosphorylase b and increased amylo-1,6-glucosidase activity. (2) GSD VI was characterized by a normal or increased phosphorylase kinase activity, a slight activation of endogenous phosphorylase b and a normal amylo-1,6-glucosidase activity.

Child↗
PubMed1976

The role of the glucose-6-phosphate in the phosphorylase b kinase activation found in perfused rat hearts treated by dinitrophenol.

In order to explain the phosphorylase b kinase activation found in perfused rat hearts treated by dinitrophenol, the glucose-6-phosphate levels and the enzyme activity were determined. Experiments were also done to determine the phosphorylase b kinase inhibition by the ester. The low glucose-6-phosphate levels and the enzyme inhibition found, suggested that the phosphorylase b kinase is activated by a mechanism that involves phosphofructokinase.

Animals↗
PubMed1989

The effect of ethanol on glucose production in phosphorylase b kinase deficiency.

Glucose production was measured using stable isotopic techniques in two patients with phosphorylase b kinase deficiency before and after oral ethanol (0.75 g/kg). Glucose production was normal before the ethanol. In one patient, who did not take the full dose of ethanol, glucose production rose initially and then fell. In the other, glucose production fell steadily and in both patients blood lactate concentrations rose. Blood glucose concentrations decreased. Patients with this enzyme deficiency are dependent on the gluconeogenic pathway when fasting and, therefore, ethanol may be potentially hazardous.

Adolescent↗
PubMed1979

Hormonally specific expression of cardiac protein kinase activity.

The relationship between the effects of isoproterenol and prostaglandin E(1) (PGE(1)) on contractile state, cyclic AMP accumulation, and the activation states of protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37), phosphorylase kinase, glycogen synthase, and glycogen phosphorylase have been studied in the isolated perfused rat heart. Perfusion of hearts with isoproterenol (10 or 80 nM) caused enhancement of left ventricular dP/dt (P, pressure), increased intracellular cyclic AMP, increased the activation states of protein kinase, phosphorylase kinase, glycogen phosphorylase, and conversion of glycogen synthase to a less active form. PGE(1) (2 or 30 muM) increased cyclic AMP accumulation and activated protein kinase, but caused no detectable changes in dP/dt or the activation states of the protein kinase substrates involved in glycogen metabolism. Perfusion of hearts with either 10 nM isoproterenol or 30 muM PGE(1) produced comparable increases in cyclic AMP accumulation and protein kinase activity. Exposure of hearts to a combination of these agents caused additive effects on cyclic AMP content and protein kinase activity. However, values for phosphorylase kinase, glycogen phosphorylase, glycogen synthase, and dP/dt did not differ from those observed in the presence of 10 nM isoproterenol alone. The failure of PGE(1) to stimulate phosphorylation of protein kinase substrates was not due to an increase in phosphorylase phosphatase activity. We conclude that an increase in intracellular cyclic AMP and the subsequent activation of protein kinase are insufficient to change either the activities of phosphorylase kinase, glycogen phosphorylase, and glycogen synthase or the inotropic state of heart muscle.

Animals↗
PubMed1997

A study of supramolecular organization of glycogenolytic enzymes in vertebrate muscle tissue.

Under conditions preventing the direct binding of phosphorylase kinase to glycogen, we detected the formation of the compound ternary complex of glycogen, phosphorylase and phosphorylase kinase. The complex formation occurs in two stages: (i) the formation of phosphorylase-glycogen complex controlled by ATP, (ii) the binding of phosphorylase kinase to the previously formed phosphorylase-glycogen complex exclusively in the presence of Ca2+ and Mg2+. The process is responsible for the increase of phosphorylase kinase activity in the presence of glycogen. An opinion is offered that a specific order of enzyme binding to glycogen particle as support provides for a self-assembly of the studied metabolon and plays an essential role in the regulation of glycogenolysis.

Animals↗
PubMed1995

Phosphorylase b kinase deficiency glycogenosis with cirrhosis of the liver.

We describe an Arab girl with complete absence of phosphorylase b kinase activity in the liver, symptomatic hypoglycemia, and persistently elevated serum aminotransferase values whose symptoms did not lessen with age; sequential liver biopsies showed progression to cirrhosis. Cirrhosis could not be ascribed to any other known cause. We conclude that type IX glycogenosis is not always associated with a benign outcome.

Child, Preschool↗
PubMed1986

Age-related augmentation of phosphorylase b kinase in hepatic tissue from the glycogen-storage-disease (gsd/gsd) rat.

The effects of food deprivation on body weight, liver weight, hepatic glycogen content, glycogenolytic enzymes and blood metabolites were compared in young and old phosphorylase b kinase-deficient (gsd/gsd) rats. Although the concentration of glycogen in liver from 9-week-old female gsd/gsd rats (730 mumol of glucose equivalents/g wet wt.) was increased by 7-8% during starvation, total hepatic glycogen was decreased by 12% after 24 h without food. In 12-month-old male gsd/gsd rats the concentration of liver glycogen (585 mumol of glucose equiv./g wet wt.) was decreased by 16% and total hepatic glycogen by nearly 40% after food deprivation for 24 h. Phosphorylase b kinase and phosphorylase a were present at approx. 10% of the control activities in 9-week-old gsd/gsd rats, but both enzyme activities were increased more than 3-fold in 12-month-old affected rodents. It is concluded that the age-related ability to mobilize hepatic glycogen appears to result from the augmentation of phosphorylase b kinase during maturation of the gsd/gsd rat.

Aging↗
PubMed1981

Alkalinization of phosphorylase kinase-deficient muscle during tetanic contraction.

The intracellular pH of resting and stimulated muscle was monitored by two independent methods: measurement of pH in iodoacetate-treated homogenates of freeze-clamped tissue and the absorbance at 550-443 nm of intracellular neutral red dye in vivo. During tetanic stimulation, muscle of phosphorylase kinase-deficient mice shows a transient alkalinization whereas muscle in normal mice becomes more acid under similar conditions. The alkalinization appears to be caused by abnormally rapid AMP deamination associated with adaptation to phosphorylase kinase deficiency.

Animals↗
PubMed1982

Fructose-2,6-P2, chemistry and biological function.

A new activator of phosphofructokinase, which is bound to the enzyme and released during its purification, has been discovered. Its structure has been determined as beta-D Fructose-2,6-P2 by chemical synthesis, analysis of various degradation products and NMR. D-Fructose-2,6-P2 is the most potent activator of phosphofructokinase and relieves inhibition of the enzyme by ATP and citrate. It lowers the Km for fructose-6-P from 6 mM to 0.1 mM. Fructose-6-P,2-kinase catalyzes the synthesis of fructose-2,6-P2 from fructose-6-P and ATP, and the enzyme has been partially purified. The degradation of fructose-2,6-P2 is catalyzed by fructose-2,6-bisphosphatase. Thus a metabolic cycle could occur between fructose-6-P and fructose-2,6-P2, which are catalyzed by these two opposing enzymes. The activities of these enzymes can be controlled by phosphorylation. Fructose-6-P,2-kinase is inactivated by phosphorylation catalyzed by either cAMP dependent protein kinase or phosphorylase kinase. The inactive, phospho-fructose-6,P,2-kinase is activated by dephosphorylation catalyzed by phosphorylase phosphatase. On the other hand, fructose-2,6-bisphosphatase is activated by phosphorylation catalyzed by cAMP dependent protein kinase. Investigation into the hormonal regulation of phosphofructokinase reveals that glucagon stimulates phosphorylation of phosphofructokinase which results in decreased affinity for fructose-2,6-P2 appears to be due to the decreased synthesis by inactivation of fructose-2,6-P2,2-kinase and increased degradation as a result of activation of fructose-2,6-bisphosphatase. Such a reciprocal change in these two enzymes has been demonstrated in the hepatocytes treated by glucagon and epinephrine. The implications of these observations in respect to possible coordinated controls of glycolysis and glycogen metabolism are discussed.

Enzyme Activation↗
PubMed1986

Features of glycogen phosphorylase from the body wall musculature of the lugworm Arenicola marina and the mode of activation during anoxia.

The activities of glycogen phosphorylases a and b from the body wall musculature of the marine worm Arenicola marina (Annelida, Polychaeta) were determined after various periods of anoxia. Already under normoxic conditions one third of the total activity was produced from the a form. During anoxia the ratio of both forms as well as the total activity did not change. The activity of soluble phosphorylase kinase was comparatively low in this tissue 4.3 +/- 1.2 nmol . min-1 . (g wet wt.)-1; the fast twitching tail muscle of shrimps, e.g., had a 10-fold higher phosphorylase kinase activity, whereas phosphorylase activities in both tissues were about the same 2.3 +/- 0.5 mumol . min-1 . (g wet wt.)-1. Glycogen phosphorylase b was purified from the body wall tissue of the marine worm in one step by 5'-AMP-Sepharose resulting in a single protein band in SDS-PAGE. This preparation was accepted as substrate by the phosphorylase kinase from rabbit muscle but a complete phosphorylation could not be achieved. The molecular mass of native phosphorylase was approximately 216 kDa, that of subunits 95 kDa indicating that the enzyme exists as a dimer. There were no isozymes in this preparation, the RF-value (0.17) of the single band in PAGE ranged between those of the isozymes from mice hearts. The activities of phosphorylases b and a were similarly dependent on pH and temperature but differed drastically in the affinities to phosphate and AMP. In presence of 1 mM AMP the app. Km of phosphorylase a for phosphate was 16 mM, that of phosphorylase b above 100 mM.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Monophosphate↗
PubMed1983

Purification and properties of phosphorylase from baker's yeast.

A rapid, reliable method for purification of phosphorylase, yielding 200-400 mg pure phosphorylase from 8 kg of pressed baker's yeast, is described. The enzyme is free of phosphorylase kinase activity but contains traces of phosphorylase phosphatase activity. Phosphorylase constitutes 0.5-0.8% of soluble protein in various strains of yeast assayed immunochemically. The subunit molecular weight (Mr) of yeast phosphorylase is around 100,000. The enzyme is composed of two subunits in various ratios, differing slightly in molecular weight and N-terminal sequence. Both are active. Only the enzyme species containing the larger subunit can form tetramers and higher oligomers. The activated enzyme is dimeric. Correlated with specific activity (1 to 110 U/mg), phosphorylase contained between less than 0.1 to 0.74 covalently bound phosphate per subunit. Inactive forms of phosphorylase could be activated by phosphorylase kinase and [gamma-32P]ATP with concomitant phosphorylation of a single threonine residue in the aminoterminal region of the large subunit. The small subunit was not labeled. The incorporated phosphate could be removed by yeast phosphorylase phosphatase, resulting in loss of activity of phosphorylase, which could be restored by ATP and phosphorylase kinase.

Enzyme Activation↗