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At least 1,063 records · Page 59Linked to original sources
PubMed1985

Calcium- and calmodulin-dependent phosphorylase kinase activity in porcine uterine smooth muscle.

Porcine uterine smooth muscle phosphorylase kinase has been partially purified. The enzyme was activated about 1.5-2.0-fold by exogenous calmodulin. Half maximal stimulation was observed at about 100 nM calmodulin. The activation was dependent on calcium and was maximum at pH 7.5 in the range of pH from 6 to 9. This activation was completely abolished by 100 microM trifluoperazine. The result suggested that unlike slow and cardiac muscles, phosphorylase kinase of uterine smooth muscle showed similar response to calmodulin with that of fast muscle. The physiological role of the calcium and calmodulin-dependent activation of myometrium phosphorylase kinase is briefly discussed.

Animals↗
PubMed1985

Inhibition of phosphorylase kinase, and tyrosine protein kinase activities by quercetin.

Quercetin, a naturally occurring bioflavonoid inhibited the activities of phosphorylase kinase and a partially purified tyrosine protein kinase from rat lung. The inhibition was rapid and concentration dependent. Quercetin at 100 microM inhibited the activities of phosphorylase kinase and tyrosine protein kinase by about 95 and 80-90 percent respectively. ATP reversed the quercetin mediated inhibition of tyrosine protein kinase but not of phosphorylase kinase. These data suggest that quercetin has differential effect on different protein kinase activities and it may be used as a tool to probe the role of various protein kinases in cell function.

Adenosine Triphosphate↗
PubMed1991

Cleavage of phosphorylase kinase and calcium-free calmodulin by HIV-1 protease.

Phosphorylase kinase and calcium-free calmodulin are digested by human immunodeficiency virus-1 protease. In phosphorylase kinase, the alpha subunit is preferentially hydrolyzed at arg748-val749. The beta subunit is cleaved only slowly at leu678-pro679, and calmodulin, the integral delta subunit of phosphorylase kinase, is not cleaved at all. However, free calmodulin in the calcium-depleted form showed to be a good substrate for the protease. Here the cleavage occurs at phe65-pro66 and met71-met72. This fast hydrolysis of free calmodulin can be blocked by micromolar concentrations of Ca2+ or millimolar concentrations of Mg2+.

Amino Acid Sequence↗
PubMed1991

Phosphorylase kinase activity in I/strain neonatal skeletal muscle with a deficiency in alpha/alpha' subunit mRNAs.

In the adult I/LnJ mouse skeletal muscle, phosphorylase kinase activity is 0.2% of that in normal. This deficiency results from a paucity of mRNA's for the phosphorylase kinase regulatory subunit- alpha and its isoform alpha'. However, in the I/LnJ neonatal skeletal muscle phosphorylase kinase activity is 20-25% of that in normal. During the first two months of development this activity decreases while in normal tissue it increases. The developmental differences in the magnitude of the I/LnJ deficiency indicate the possibility of stage specific mechanisms regulating the accumulation of alpha/alpha' mRNAs. To investigate this possibility, the abundance of alpha/alpha' mRNAs and of the catalytic subunit, gamma, mRNAs were compared by Northern Blot analysis. The results demonstrate that neonatal and adult I/LnJ skeletal muscle have a similar paucity of alpha/alpha' mRNAs whereas accumulation of gamma mRNAs is not significantly different from normal.

Aging↗
PubMed1991

Amylin activates glycogen phosphorylase and inactivates glycogen synthase via a cAMP-independent mechanism.

Although the novel pancreatic peptide amylin has been shown to induce insulin resistance and decrease glucose uptake, the mechanism of amylin's actions is unknown. The following study evaluated the effect of amylin on glycogen metabolism in isolated soleus muscles in the presence and absence of insulin (200 microU/ml). Total glycogen, glycogen phosphorylase and glycogen synthases activities, and cAMP levels were measured. Total glycogen levels were significantly decreased by amylin (100 nM) in fed or fasted muscles under conditions of insulin stimulation. Amylin (100 nM) activated glycogen phosphorylase by as much as 100% and decreased glycogen synthase activity by over 60%, depending on the metabolic state of the muscles. These effects where comparable to those of the beta adrenergic agonist isoproterenol. A lower concentration of amylin (1 nM) did not significantly affect glycogen levels, glycogen phosphorylase, or glycogen synthase activity. Cyclic AMP levels were increased two-fold by isoproterenol but were unaffected by amylin. In conclusion, amylin induces glycogenolysis by decreasing glycogen synthesis and increasing breakdown. The effect of amylin on enzyme activity is consistent with a phosphorylation-dependent mechanism. It is likely that these events are mediated via a cAMP independent protein kinase.

Amyloid↗
PubMed1987

Inhibitor properties of some 5-substituted uracil acyclonucleosides, and 2,2'-anhydrouridines versus uridine phosphorylase from E. coli and mammalian sources.

Two series of 5-substituted uracil N(1)-acyclonucleosides, each with a different acyclic chain, were examined as inhibitors of uridine phosphorylase from rat intestinal mucosa, and several against the enzyme from Ehrlich ascites cells. In addition, several 5-substituted analogues of 2,2'-anhydrouridine were tested for their inhibitory effects vs a highly purified uridine phosphorylase from Escherichia coli. The results are compared with previously published data for inhibition of the E. coli enzyme by the acyclonucleosides, and of the rat enzyme by the anhydrouridines. In all instances, the inhibitors were active only vs the uridine, but not thymidine, phosphorylase from E. coli, and inhibition was competitive with respect to uridine as substrate. In general, with one or two exceptions, inhibitory effects were more pronounced against the enzyme from mammalian sources. Amongst the acyclonucleoside analogues, the most effective inhibitor of the enzyme from the rat and Ehrlich ascites cells exhibited a Ki = 0.1 microM, comparable to that reported with the Sarcoma-180 enzyme, whereas the Ki for inhibition of the E. coli enzyme was 0.7 microM. By contrast, another effective inhibitor of the bacterial enzyme was 7-fold less potent against the mammalian enzyme. The 2,2'-anhydrouridines were 10- to 30-fold more effective against the rat, as compared to the E. coli, enzyme. The overall quantitative data provide a reasonably good basis for the further design of potent inhibitors for possible use in chemotherapy.

Animals↗
PubMed1990

Circadian rhythm of hepatic uridine phosphorylase activity and plasma concentration of uridine in mice.

The activity of hepatic uridine phosphorylase (EC 2.4.2.3.) in male mice (24-29 g) maintained in standardized conditions of 12 hr light (0600-1800 hr) alternating with 12 hr darkness (1800-0600 hr), food and water ad lib., exhibited a circadian rhythm (P less than 0.0001, Cosinor analysis). The peak of enzyme activity (559 +/- 25 pmol/min/mg protein) occurred at 15 hr after light onset (HALO) with the nadir (139 +/- 25 pmol/min/mg protein) at 3 HALO when samples were taken every 4 hr. Female mice showed essentially the same pattern. A circadian rhythm (P less than 0.0001, Cosinor analysis) was also observed when the light-dark cycle was shifted (reverse cycle) so that the lights went on at 2200 hr and off at 1000 hr. Under the reverse cycle condition, there was a corresponding shift in the enzyme activity with a lag period of 3.5 hr in the time of maximum and minimum enzyme activities (i.e. the peak at 11 HALO and the nadir at 23 HALO) after a 2-week adaptation period. The lag period was reduced to 1 hr after 4 weeks of adaptation, and no further change was observed after 6 weeks of adaptation. The plasma concentration of uridine also exhibited a circadian rhythm (P less than 0.0001, Cosinor analysis) with peak concentration (10 microM) occurring at 2 HALO and a nadir (5 microM) at 14 HALO. The circadian rhythm observed in the plasma concentration of uridine is the inverse of that for uridine phosphorylase activity. These results demonstrate that hepatic uridine phosphorylase plays an important role in the regulation of the uridine level in the blood which, in turn, may be involved in the humoral control of sleep by uridine. This may also be of clinical significance in enhancing the antitumor efficacy of the 5-fluorinated pyrimidines by modulating the time of their administration.

Animals↗
PubMed1976

An abnormal form of purine nucleoside phosphorylase in a family with a child with severe defective T-cell-and normal B-cell immunity.

1. Purine nucleoside phosphorylase and adenosine deaminase (ADA) were studied in normal red blood cells and lymphocytes and in the cells of a family with a child with a defective T-cell-and normal B-cell immunity. 2. In the propositus no purine nucleoside phosphorylase (NP) activity could be detected in her red cells and lymphocytes, while the ADA activity was somewhat increased. The NP activities of the father, mother and brother of the propositus are in the heterozygote range. The decreased activity of NP was not only found for the substrate inosine but also when guanosine or xanthosine were used as substrate. The mode of inheritance is autosomal recessive. 3. With starch gel electrophoresis no NP activity could be detected in the patient's haemolysate. The electrophoretic patterns of NP from the father, mother and brother of the patient seem to be the same as for normal NP with six bands of NP activity. 4. The nucleoside phosphorylases of the father, mother and brother of the patient were characterized by an increased KM for the substrate inosine, normal pH optimum and a decreased heat stability.

Adenosine Deaminase↗
PubMed1981

A rapid and simple radiometric assay for thymidine phosphorylase of human peripheral blood cells.

A radiometric method is described for measuring thymidine phosphorylase activity in human peripheral blood cells. The substrates [14C]thymidine or [14C]thymine are converted to the base or deoxynucleoside, respectively, and two alternative chromatographic methods to isolate the products of the reaction have been employed. With the described methods the specific activity for thymidine phosphorylase in human lymphocytes is 0.21 +/- 0.08; monocytes 0.21 +/- 0.16 and granulocytes 0.17 +/- 0.02 mu mol.h-1.mg-1 protein. For human T- or null lymphoblasts, thymidine phosphorylase activity was found to be approximately 10% of that of B lymphoblasts.

Blood Platelets↗
PubMed1977

Stimulation of cardiac sarcolemmal (Na+--K+) ATPase activity by phosphorylase kinase.

Following preincubation with phosphorylase kinase, ATPase activities of heart sarcolemmal membranes were increased: total ATPase from 9.38+/-0.65 to 15.25+/-0.90 and ouabain-sensitive (Na+--K+)ATPase from 1.67+/-0.17 to 3.12+/-0.33 micron moles Pi/mg protein/h (mean +/- S.E. of 3 experiments); (Ca2+)ATPase and (Mg2+--Ca2+)-ATPase activities were not significantly altered due to phosphorylase kinase. Under these conditions, phosphorylase kinase catalyzed phosphorylation of sarcolemmal membranes. The kinase-catalyzed phosphorylation of membranes was increased by Ca2+ ions: at pH 6.8, 30% increase in phosphorylation was observed whereas at pH 8.5, 267% increase was noted due to this action. These findings support the view that Ca2+-dependent phosphorylation of membranes regulates (Na+--K+)ATPase.

Adenosine Triphosphatases↗
PubMed1983

Calcium--calmodulin-dependent activation of porcine liver phosphorylase kinase.

Porcine liver phosphorylase kinase was activated about 1.5-fold by calmodulin in a calcium-dependent manner. Half-maximal stimulation was observed at about 80 nM calmodulin and the activation was almost pH-independent. The specific binding of porcine liver phosphorylase kinase to calmodulin--Sepharose affinity column exhibited an absolute dependence upon the presence of calcium. The physiological role of the calmodulin-dependent activation for liver phosphorylase kinase is discussed.

Animals↗
PubMed1984

Two diverse effects of poly(L-lysine) on rabbit skeletal muscle phosphorylase kinase: stimulation of autophosphorylation and inhibition of its activity.

Polylysine greatly stimulated the autophosphorylation of phosphorylase kinase from rabbit skeletal muscle. When fully autophosphorylated, about 14 mol of phosphate per tetramer (alpha beta gamma delta) were incorporated in the presence of polylysine, which was twice as much as those observed without polylysine. In contrast to this stimulatory effect of polylysine on the autophosphorylation, polylysine strongly inhibited the conversion reaction of phosphorylase b to a. The inhibition is competitive with a Ki of 2.3 micrograms/ml. No effects of polylysine were observed on the activities of phosphorylase and cAMP-dependent protein kinase.

Animals↗
PubMed1990

A low-molecular weight acid phosphatase present in crystalline preparations of rabbit skeletal muscle glycogen phosphorylase b.

Crystalline preparations of glycogen phosphorylase b contain traces of acid phosphatase activity. Non-denaturing gel electrophoresis of phosphorylase b reveals a single band of 1-naphthyl phosphate phosphohydrolase activity which co-migrates with phosphorylase. The two enzymes can be separated by Sephadex G-200 column chromatography, where the phosphatase exhibits an apparent Mr of 17,000. The contaminant enzyme hydrolyzes effectively the phenolic ester of monoorthophosphate with optimal activity for p-nitrophenyl phosphate and L-phosphotyrosine between pH 5.5 and 6.0. The phosphatase is insensitive to inhibition by L(+)-tartrate but strongly inhibited by microM vanadate and Zn2+.

Acid Phosphatase↗
PubMed1992

Glucose has to be phosphorylated to activate glycogen synthase, but not to inactivate glycogen phosphorylase in hepatocytes.

2-Deoxyglucose and 5-thioglucose, in the same fashion as glucose, cause the inactivation of the rat hepatocyte glycogen phosphorylase and the activation of glycogen synthase. However, 6-deoxyglucose and 1,5-anhydroglucitol inactivate phosphorylase without increasing the activation state of glycogen synthase. With 3-O-methylglucose no changes in the activity of these enzymes occurred. These results prove that while glucose is the molecule that triggers the inactivation of phosphorylase, glucose 6-phosphate is the signal for glucose synthase activation and that a metabolite control of the activation state of glycogen synthase is operative in hepatocytes.

Animals↗
PubMed1992

Transforming growth factor-beta 1 rapidly activates phosphorylase in a calcium-dependent manner in rat hepatocytes.

Transforming growth factor-beta 1 (TGF-beta 1) rapidly activated phosphorylase in isolated rat hepatocytes (half-maximal rate of activation with approximately 0.1 ng/ml). Removal of Ca2+ from the external medium just before TGF-beta 1 addition markedly attenuated phosphorylase activation. TGF-beta 1 (1 ng/ml) produced a small increase in [Ca2+]i (approximately 10% increase after 30 s), which appears sufficient to account for phosphorylase activation. These observations indicate that activation of the TGF-beta 1 signal transduction system in hepatocytes is linked with a small increase in [Ca2+]i, and external Ca2+ may contribute in part to this increase.

Animals↗
PubMed1988

Hormonal regulation of fat body glycogen phosphorylase activity in larval Manduca sexta during starvation.

The hormonal regulation of fat body glycogen phosphorylase activity in Manduca sexta larvae was studied. During the first 3 hr of starvation the corpora cardiaca (CC) release a glycogen phosphorylase-activating hormone (GPAH). The haemolymph of 24-hr-starved larvae seems to contain increased levels of GPAH, but after 48 hr the titre can be assumed to be as low as prior to starvation. Abdominal stretch receptors do not appear to be involved in the regulation of GPAH release from the CC. Phosphorylase activation can be prevented by the injection of glucose or by feeding the animals with agar containing various carbohydrates. These treatments seem to prevent the release of GPAH from the CC rather than the action of GPAH on the fat body. The physiological signal which initiates peptide release remains unclear.

Animals↗
PubMed1990

Regulatory properties of rabbit liver phosphorylase kinase.

1. Purified native rabbit liver phosphorylase kinase becomes activated during the assay of its activity while low molecular weight forms of the same enzyme do not. 2. The activation requires ATP and magnesium ions, suggesting the phosphorylation of the enzyme by a protein kinase as the mechanism involved. 3. The activation of the enzyme can be reverted by the action of a type I protein phosphatase isolated from the same tissue. 4. The activation can also be catalyzed by the catalytic subunit of cAMP-dependent protein kinase in a process that requires a much lower ATP concentration to proceed. 5. The activation is believed to be due to an autocatalytic phosphorylation of phosphorylase kinase itself. In support of this hypothesis are the regulation of the process through calcium ions, the low levels of endogenous protein kinase detected in the purified preparation, the high ATP concentrations required in the absence of cAMP dependent protein kinase and the fact that the process cannot be blocked by an excess of the heat stable inhibitor specific for the later enzyme. 6. The low molecular weight forms of the enzyme on their side are not affected by the action of neither protein phosphatase 1 nor cyclic AMP dependent protein kinase. 7. Both activated and nonactivated phosphorylase kinase are partially dependent on calcium ions, the affinity of the former being higher than that of the latter. The low molecular forms do not require calcium ions to express their activity.

Adenosine Triphosphate↗
PubMed1992

Lack of oscillations in cyclic AMP, cAMP-protein kinase and glycogen phosphorylase during the cardiac cycle in perfused rat hearts.

It is unclear whether reported fluctuations in the level of adenosine 3',5'-cyclic monophosphate (cAMP) during a single cardiac cycle in ventricular muscle are associated with distal changes in cAMP-dependent processes. The degree of cAMP variation and its effect, if any, on biochemical sequelae during the cardiac cycle, were investigated by determining the level of cAMP and the activity ratios of cAMP-dependent protein kinase and glycogen phosphorylase in the rat ventricular myocardium. Isolated perfused hearts contracting at 240 beats/min and free of exogenously administered catecholamines were freeze-clamped, utilizing an automated clamping device capable of freezing the entire heart in less than 50 ms. The cardiac cycle was segmented into phases utilizing three different segmentation schemes. No significant difference was detected between phases regardless of the method of segmentation for cAMP, cAMP-dependent protein kinase, or glycogen phosphorylase levels. These results suggest that the levels of cAMP and the activities of cAMP-dependent protein kinase and glycogen phosphorylase do not vary significantly during a single cardiac cycle in the mammalian myocardium.

Animals↗