Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01275 (glucagon)
 26,492 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of carbamylcholine (Cch), the divalent cation ionophore A23187 and Ca2+ on the cyclic 3',5'-guanosine monophosphate (cGMP) and cyclic 3',5'-adenosine monophosphate (cAMP) content of rat renal cortical slices were examined. In both the presence and absence of 10 mM theophylline, Cch detectably increased cGMP within 15 sec, with peak responses noted by 2 min. The maximal cGMP response to Cch alone (0.05 mM) was an increase of two- to three-fold over control. Theophylline, which was routinely present in the incubations and which alone increased cGMP of the slices two-fold over basal during 20 min incubations, potentiated the response to Cch (maximal increase, five- to sixfold over theophylline alone). The action of Cch to increase renal cortical cGMP was blocked by prior addition of atropine and was dependent upon the presence of Ca2+ in the incubation media. Exclusion of Ca2+ lowered basal cGMP and abolished increases mediated by Cch, while exclusion of Mg2+ was without detectable effect on cGMP. In slices incubated initially without Ca2+, reexposure to Ca2+ for 1min partially restored the cGMP response to Cch, and reexposure for 3 min completely restored this response. Since prior incubation of tissue in Ca2+-free buffer for only 2 min was sufficient to block the cGMP responses to Cch, depletion of tissue Ca2+ did not appear to be involved. A23187 also increased renal cortical cGMP fivefold in the presence of Ca2+. Its effects were not additive with those of Cch and were not additive with those of Cch and were not expressed by Mg2+ in Ca2+-free media. By contrast, tetracaine, which blocks Ca2+ transport across or binding to biologic membranes, reduced basal cGMP and inhibited the actions of Cch and A23187 to increase cGMP in cortical slices incubated with Ca2+. The action of 1 mM tetracaine to block Cch-mediated increases in cGMP was partially reversed by increasing media Ca2+ from 1.5 to 5 mM, but not by increasing media Mg2+ to 5 mM. In contrast to their effects on cGMP, Cch, A23187, Ca2+ exclusion, and tetracaine did not detectably alter basal renal cortical cAMP or cAMP responses to parathyroid hormone (PTH). Conversely, concentrations of PTH, glucagon, and isoproterenol which maximally increased renal cortical cAMP did not alter cGMP. Furthermore, prior incubation of slices with Cch did not alter their subsequent cAMP response to PTH at a time when cGMP levels were still elevated, while prior incubation with PTH did not affect the subsequent cGMP response to Cch at a time when cAMP was increased. These studies demonstrate modulation of renal cortical cGMP by cholinergic stimuli and Ca2+. They also indicate that cGMP and cAMP in renal cortex can be regulated independently.
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PMID:Calcium-dependent regulation of guanosine 3',5'-monophosphate in renal cortex: effects of ionophore A23187 and tetracaine and evidence for independent control of adenosine 3',5'-monophosphate. 18 65

The glycogen pellet of dog liver extracts contains a phosphorylase phosphatase which has characteristics different from those of the phosphatases extracted from the cytosol. The phosphatase associated with glycogen is characterized by a M, of 51,000, a half maximal inhibition at 0.3 mM ATP (Hill coefficient : 2) and a Ki for Mg2+ of 1 mM. Treatment with urea or mercaptoethanol of the phosphatase associated with glycogen does not influence the activity, the Mr or the half maximal inhibition by ATP, but a decrease of the Hill coefficient for ATP is observed. A similar treatment of the phosphatases extracted from the high speed supernatant results in a decrease of the Mr of the spontaneously active form from 215,000 to 43,000, without an effect on the Ki for ATP (7 micronM), but accompanied by an increase in activity. The ATP-Mg dependent form of the phosphatase from the high speed supernatant (Mr : 138,000 ; Ka for ATP in the presence of 0.1 mM Mg2+ : 0.3 micronM), is denatured by urea or mercaptoethanol. The phosphatase associated with particulate glycogen cannot be found in the supernatant, nor the phosphorylase phosphatases present in the supernatant in the glycogen pellet. When all the glycogen is mobilized (starvation, glucagon) the phosphatase specifically associated with glycogen cannot be found as such in the cytosol. No activation of synthase beta can be detected neither with the phosphatases extracted from the cytosol nor with the enzyme released from the glycogen pellet.
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PMID:Multiple molecular forms of phosphorylase phosphatase associated with particulate glycogen and extracted from the cytosol of dog liver. 19 25

In normal fed rats, glycogen synthase D phosphatase activity in a glycogen pellet preparation was only partially inhibited (approximately 50%) by high concentrations of EDTA. However, the proportion of phosphatase activity inhibited by EDTA was markedly and rapidly (15 s) increased following glucagon or cAMP administration. Epinephrine administration did not alter the proportion of activity inhibited by EDTA. Glucose administration rapidly (2 min) reduced the proportion of synthase phosphatase activity inhibitable by EDTA. That is, the effect of glucose was just the opposite of that produced by glucagon or cAMP. Insulin administration had no effect on phosphatase activity. Synthase phosphatase activity assayed in the absence of EDTA was similar in all groups except for a moderate increase after glucose administration. Addition of Mg2+ completely reversed EDTA inhibition. Phosphorylase phosphatase activity in each group was not modified by addition of EDTA, although the percentage of phosphorylase in the alpha form was higher in glucagon-treated and lower in the glucose-treated animals as expected. These data suggest the presence of rapidly interconvertible forms of either synthase phosphatase or its substrate synthase D, detectable as a change in EDTA inhibitability and subject to glucose and glucagon control.
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PMID:In vivo glucose-, glucagon-, and cAMP-induced changes in liver glycogen synthase phosphatase activity. 20 88

The kinetic characteristics of substrate utilization by hepatic adenylate cyclase were investigated under a variety of incubation conditions, including veriations in pH, [substrate], [Mg2+], and in the absence or presence of glucagon. Activities were compared with ATP and 5'-adenylylimidodiphosphate (App(NH)p) as substrates. The Km for both substrates was about 50 muM; Vmax given with App(NH)p was about 40% lower than obtained with ATP as substrate. In the presence of a saturating concentration of substrate (1 mM), basal activity was increased 4-fold by increasing [Mg2+] from 5 to 50 mM. The stimulatory effect of Mg2+ was not due to an allosteric action since basal activity was only marginally enhanced (40%) when the substrate concentration was reduced to 10 muM. As suggested by deHaen ((1974 J. Biol. Chem. 249, 2756), it is likely that Mg2+ increases enzyme activity by decreasing the concentration of an inhibitory, unchelated form of substrate that competes with the productive magnesium-substrate complex at the active site. Activity-pH profiles differed with ATP and App(NH)p as substrates; a shift in pH optimum was observed which correlated with the different pKa of the terminal phosphate groups of ATP and App(nh)p, and which reflect the concentration of protonated substrate (ATPH-3 minus) present in the incubation medium. Accordingly, protonated substrate is the predominant inhibitory species of unchelated substrate and probably has a considerably higher affinity for the active site than does the magnesium-substrate complex. Glucagon-stimulated activity was less susceptible to inhibition by protonated substrate than is the basal state as evidenced by lower stimulatory effect when the [Mg2+] was increased from 5 to 20 mM. However, increasing the [Mg2+] from 20 to 50 mM resulted in marked inhibition of glucagon-stimulated activity, particularly in the presence of 10 muM substrate. Conversely, at a fixed [Mg2+], concentrations of substrate at least 20-fold higher than the Km were required to achieve maximal hormone-stimulated activity. These findings suggest that the unchelated, fully ionized form of substrate serves as an activating ligand, as has been observed with guanine nucleotides at considerably lower concentrations. Thus, Mg2+ affects adenylate cyclase activity by forming the productive substrate complex and by titrating the inhibitory protonated and activating free forms of substrate. As a result of these effects of unchelated substrate, it proved difficult to evaluate the kinetic parameters involved in substrate binding and utilization and the effects of hormone thereon when substrate was added as the only source of activating ligand. However, linear Michaelis kinetic data were obtained by adding the activating ligand 5'-guanylylimidodiphosphate with glucagon and by making appropriate adjustments of pH and [Mg2+]. Vmax was increased 4-fold without changes in Km by the actions of 5'-guanylylimidodiphosphate and glucagon.
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PMID:The hepatic adenylate cyclase system. II. Substrate binding and utilization and the effects of magnesium ion and pH. 23 15

Adenylate cyclase activity in purified plasma membranes from rat fat cells displays transient kinetic characteristics in the absence and presence of guanyl=5'=yl imidodiphosphate (Gpp(NH)p). Gpp(NH)p causes immediate inhibition of enzyme activity; the inhibitory phase is followed by a slow increase in activity which, depending on incubation temperature, exceeds activity stimulated in the presence of hormones (glucagon, secretin, epinephrine, or adrenocorticotropin). Basal activity displays an initial high rate of activity which decays to a low state of activity within 2 min of incubation. Hormones do not alter the initial rate but prevent the decay in enzyme activity. The inhibitory phase of Gpp(NH)p action and the previously reported (Harwood, J.P., Low, H., and Rodbell, M. (1973) J. Biol. Chem. 248, 6239-6245) inhibitory effects of GTP are abolished by increasing (Mg2+) and pH to 50 mM and 8.5, respectively. Under these conditions, Gpp(NH)p and GTP cause marked stimulation of activity, the stimulatory effect of Gpp(NH)p being greater than that of GTP both in the absence and presence of hormones...
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PMID:On the mechanism of activation of fat cell adenylate cyclase by guanine nucleotides. An explanation for the biphasic inhibitory and stimulatory effects of the nucleotides and the role of hormones. 23 88

Smooth muscle adenylate cyclase of a membrane preparation of canine gastric antrum has been characterized, and the effect of hormonal and neuronal agents examined. The enzyme is active in the presence of Mg2+ or Mn2+, but is inhibited by Ca2+. The Km is 0.5 mM ATP, similar to the Km of skeletal muscle adenylate cyclase. The enzyme is activated by isoproterenol but not norepinephrine, consistent with a beta 2-catecholamine receptor-adenylate cyclase interaction. Secretin activates the enzyme in concentrations as low as 1 . 10(-11) M, while glucagon was effective only at 1 . 10(-6) M. Prostaglandin E1 and E2 have a biphasic effect with activation of adenylate cyclase at 1 . 10(-5) M and a small but significant inhibition of enzyme activity at 1 . 10(-11) M.
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PMID:Effect of hormonal and neuronal agents on adenylate cyclase from smooth muscle of the gastric antrum. 45 75

Incubation of hepatocytes with [32P]orthophosphate resulted in the incorporation of 32P into material that is precipitated by reaction with antibodies to ATP citrate lyase. The amount of radioactivity precipitated was decreased when unlabeled, purified ATP citrate lyase was added to extracts of hepatocytes that had been incubated with [32P]orthophosphate. Addition of glucagon to hepatocytes that had been preincubated with [32P]orthophosphate resulted in a 56% increase in acid-stable 32P in the trichloroacetic acid-insoluble portion of immunoprecipitates. Catalytic phosphate bound to ATP citrate lyase reaction with ATP and Mg2+ is acid-labile; thus, glucagon-dependent phosphorylation is distinguished from the catalytic phosphate. When hepatocytes were incubated in the absence of [32P]orthophosphate and extracted in a medium containing [gamma-32P]ATP, no acid-stable 32P was present in immunoprecipitates. This indicates that the incorporation into ATP citrate lyase of acid-stable phosphate occurs prior to extraction of the enzyme. Preliminary studies, using a procedure that allows for measurement of enzyme activity starting 1 min after beginning the extraction of lyase from hepatocytes, have shown no difference in lyase activity when hepatocytes are treated with or without glucagon.
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PMID:Phosphorylation of ATP citrate lyase in response to glucagon. 48 38

1. Arrhenius plots of the glucagon-stimulated adenylate cyclase, 5'-nucleotidase, (Na+ + K+)-stimulated adenosine triphosphatase and Mg2+-dependent adenosine triphosphatase activities of control hamster liver plasma membranes exhibited two break points at around 25 and 13 degrees C, whereas Arrhenius plots of their activities in hibernating hamster liver plasma membranes exhibited two break points at around 25 and 4 degrees C. 2. A single break occurring between 25 and 26 degrees C was observed in Arrhenius plots of the activities of fluoride-stimulated adenylate cyclase, basal adenylate cyclase and cyclic AMP phosphodiesterase of liver plasma membranes from both control and hibernating animals. 3. Arrhenius plots of phosphodiesterase I activity showed a single break at 13 degrees C for membranes from control animals, and a single break at around 4 degrees C for liver plasma membranes from hibernating animals. 4. The temperature at which break points occurred in Arrhenius plots of glucagon- and fluoride-stimulated adenylate cyclase activity were decreased by about 7--8 degrees C by addition of 40 mm-benzyl alcohol to the assays. 5. Discontinuities in the Arrhenius plots of 4-anilinonaphthalene-1-sulphonic acid fluorescence occurred at around 24 and 13 degrees C for liver plasma membranes from control animals, and at around 25 and 4 degrees C for membranes from hibernating animals. 6. We suggest that in hamster liver plasma membranes from control animals a lipid phase separation occurs at around 25 degrees C in the inner half of the bilayer and at around 13 degrees C in the outer half of the bilayer. On hibernation a change in bilayer asymmetry occurs, which is expressed by a decrease in the temperature at which the lipid phase separation occurs in the outer half of the bilayer to around 4 degrees C. The assumption made is that enzymes expressing both lipid phase separations penetrate both halves of the bilayer, whereas those experiencing a single break penetrate one half of the bilayer only.
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PMID:Changes in the form of Arrhenius plots of the activity of glucagon-stimulated adenylate cyclase and other hamster liver plasma-membrane enzymes occurring on hibernation. 72 95

The possible role of Ca2+ in glucagon release has been investigated by the use of ionophore A23187. This ionophore permits Ca2+ entry down a suitable concentration gradient by complexing and releasing Ca2+, thereby acting as a carrier in plasma membranes. Cultured cells obtained by enzymatic digestion of pancreases from newborn rats were studied on the third day of culture. As expected the effects of the ionophore were dependent upon the presence of Ca2+ in the medium. However, either stimulation or inhibition of glucagon release resulted when different concentrations of ionophore and Ca2+ were used. With 1.0 mM Ca2+ in the medium, glucagon release was stimulated in the presence of 0.01 and 0.1 mug/ml ionophore, but inhibited in the presence of 3.0 and 10.0 mug/ml. With 0.1 mug/ml ionophore, glucagon release was stimulated by 0.3 and 1.0 mC Ca2+ but not by 2.5 mM Ca2+. With 10 mug/ml ionophore glucagon release was stimulated by 0.03, 0.1 and 0.3 mM Ca2+, whereas at 1.0 mM, glucagon release was depressed. These findings suggest that by increasing Ca2+, glucagon is released from the A-cells, whereas too large an increase in Ca2+ is inhibitory. The effect to stimulate release was not completely specific for Ca2+ in that while the ionophore did not stimulate release in the presence of either Mg2+ or Sr2+ in the absence of Ca2+, it did stimulate release when Ba2+ was tested. Furthermore Ba2+ at 0.3 mM was stimulatory even in the absence of ionophore. Glucagon release in the absence of ionophore was also enhanced by addition of 30 mM Ca2+ or by omission of Ca2+ from the medium. It is concluded that Ca2+, which plays an essential role in the stimulus-secretion coupling in several different cell types, may be involved in the stimulation of glucagon release from the A-cells of the pancreas.
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PMID:Calcium induced glucagon release in monolayer culture of the endocrine pancreas. Studies with ionophore A23187. 78 65

Adenosine inhibits the rat liver adenylate cyclase system at a regulatory site that is distinct from the glucagon receptor, the guanine nucleotide regulatory site, and the active site involved in catalysis of ATP to cyclic AMP. The effects of the nucleoside are also independent of the concentration of uncomplexed ATP (ATP4-) in the assay medium. Glucagon, but not guanine nucleotides, sensitizes the system to inhibition by adenosine. Depending on assay conditions, the hormone can shift the concentration of adenosine required for 50% inhibition by as much as 10-fold. Under optimal conditions, the apparent Ki for adenosine is 25 micron. Both Mg2+ and Mn2+ increase adenylate cyclase activity and, in order of relative potency, increase the sensitivity of the enzyme to adenosine inhibition; Mn2+ is 50- to 100-fold more potent than Mg2+. The adenosine inhibitory site exhibits stringent structural requirements for nucleoside action. Most alterations of the purine ring result in loss of activity, whereas alterations in the ribose ring are tolerated, and some deoxyadenosine analogs are even more effective than adenosine. Naturally occurring nucleosides and nucleotides, such as inosine, guanosine, and 5'-AMP, are inactive. Analog studies reveal also that inhibition of the hepatic system occurs at a site which is clearly different from the sites through which adenosine activates other adenylate cyclase systems, and that the liver enzyme appears to have no site for activation by the nucleoside.
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PMID:Regulation by glucagon and divalent cations of inhibition of hepatic adenylate cyclase by adenosine. 89 90


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