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

The glucagon analog [l-N alpha-trinitrophenylhistidine, 12-homoarginine]-glucagon (THG) was examined for its ability to lower blood glucose concentrations in rats made diabetic with streptozotocin. In vitro, THG is a potent antagonist of glucagon activation of the hepatic adenylate cyclase assay system. Intravenous bolus injections of THG caused rapid decreases (20 to 35 percent) of short duration in blood glucose. Continuous infusion of low concentrations of the inhibitor led to larger sustained decreases in blood glucose (30 to 65 percent). These studies demonstrate that a glucagon receptor antagonist can substantially reduce blood glucose levels in diabetic animals without addition of exogenous insulin.
 ...
PMID:Hyperglycemia of diabetic rats decreased by a glucagon receptor antagonist. 627 87

The photoreactive 125I-labeled glucagon-NAPS [125I-labeled 2-[2-nitro-4-azidophenyl)sulfenyl]-Trp25-glucagon] was used to label the glucagon receptor sites in rat liver plasma membranes. The proteins labeled were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with or without reduction with dithiothreitol. The photoaffinity peptide specifically labeled a number of bands with apparent molecular weights greater than 200000 and probably at least two protein bands in the molecular weight range 52000-70000. The relative amounts of radioactivity associated with these bands and their relative mobilities differed in samples from reduced and unreduced membranes. Their relative mobilities also differed with percent acrylamide cross-linking, suggesting a glycoprotein nature and the presence of intramolecular disulfide bonds. A nonspecifically labeled band with an apparent molecular weight of 27000-28000 also displayed a similar behavior. Photolabeling in the presence of 0.1 mM guanosine 5'-triphosphate (GTP) decreased the amount of radiolabeling of these bands, suggesting their involvement in the glucagon stimulation of adenylate cyclase. The photolabeled receptor in the membranes, solubilized with Lubrol-PX and fractionated on an Ultrogel AcA22 column, eluted with an apparent molecular weight of 200000-250000. Addition of GTP to the solubilized glucagon receptor of nonirradiated membranes caused complete dissociation of the complex. Gel electrophoresis of the partially purified radiolabeled receptor identified the same protein components observed in photolabeled membranes. These results indicate that the glucagon receptor is an oligomer probably composed of at least two different subunits that are linked together or greatly stabilized by disulfide bonds. They also show that 125I-labeled glucagon-NAPS can be used effectively to covalently label the putative glucagon receptor and thus aid in its further characterization.
 ...
PMID:Identification of the glucagon receptor by covalent labeling with a radiolabeled photoreactive glucagon analogue. 628 11

To evaluate the role of glucagon on its hepatocyte receptor concentrations, groups of rats were injected with a long-acting glucagon preparation (20 [G-20], 40 [G-40] or 60 [G-60] micrograms/100 g body weight) every 8 h for 4 days. Glucagon receptors in liver plasma membranes of treated animals were decreased in number (control = 1.66 +/- 0.20 ng/0.5 mg protein versus G-20 = 1.24 +/- 0.26, G-40 = 1.03 +/- 0.26, G-60 = 0.70 +/- 0.03 ng/0.5 mg protein; p less than 0.05, less than 0.001, less than 0.001, respectively), but they were indistinguishable from receptors of control rats by other criteria including affinity and kinetics of association. Degradation of both glucagon and receptor sites did not account for differences observed in binding. Similar results were obtained with isolated hepatocytes. In relation to controls, isolated hepatocytes of treated rats had a reduced number of receptors (control = 0.70 +/- 0.05 versus G-40 = 0.47 +/- 0.04 ng/10(6) cells; p less than 0.02) proportionate to the decreased glucagon-stimulated production of cyclic AMP and glucose. Four to eight hours exposure of cultured hepatocytes of nontreated rats to 4 x 10(-8) mol/l glucagon produced a decreased binding of 125I-glucagon to its receptor (p less than 0.05). In contrast, hormone exposure for shorter periods of time (0-2 h) was without effect. These results suggest (1) an inverse relationship between circulating glucagon levels and hepatocyte glucagon receptor concentration, and (2) a direct relation between receptor number and target-cell response.
 ...
PMID:Regulatory effect of glucagon on its own receptor concentrations and target-cell sensitivity in the rat. 628 78

Eighteen patients with postnecrotic cirrhosis of liver, including three patients who had had a portosystemic shunt operation, and 19 normal controls were studied. The tests performed included monocyte insulin receptor assay, iv glucose tolerance test, glucagon test, and insulin tolerance test. Insulin resistance was documented by the presence of fasting hyperglycemia and glucose intolerance together with hyperinsulinemia as well as resistance to exogenous insulin. The binding of [125I]insulin to monocyte insulin receptors was significantly decreased in cirrhotic patients compared with that in controls (P less than 0.02), and this was due to a significant decrease in the high affinity association constant (P less than 0.005). There was a significant negative correlation between the fasting insulin level and maximum [125I]insulin binding in cirrhotic patients (r = -0.8; P less than 0.02). Cirrhotics that had had a shunt operation showed a higher fasting insulin level, a greater insulin resistance, and a smaller maximum [125I]insulin binding to insulin receptors than those without shunt. All of these findings suggested a down-regulatory effect of hyperinsulinemia on the monocyte insulin receptors. An impaired glycemic response to glucagon was also found in cirrhotics, the exact mechanism of which remains to be elucidated. However, as the increases in plasma cAMP after glucagon were similar in cirrhotics and controls, the fault apparently did not lie in the glucagon receptor.
 ...
PMID:Down-regulation of insulin receptors in postnecrotic cirrhosis of liver. 628 82

N-Ethylmaleimide treatment of rat liver plasma membranes results in an adenylyl cyclase (EC 4.6.1.1) system that shows no measurable cyclizing activity but retains both an active glucagon receptor and a receptor-sensitive regulatory component N as assessed by reconstitution into cyclase-negative (cyc-) membranes from S49 murine lymphoma. Treatment of such N-ethylmaleimide-treated membranes, termed C- liver membranes, with guanosine 5'-[gamma-thio]triphosphate (GTP[gamma S] ) and Mg2+, followed by the removal of GTP[gamma S] by washing, yields an activated N which upon mixing with cyc- S49 membranes reconstitutes the cyc- S49 membrane adenylyl cyclase in the absence of added GTP[gamma S]. It was found that GTP[gamma S] activation of the N at saturating concentrations of GTP[gamma S] is slow at low Mg2+ concentration and accelerated by increasing Mg2+ concentrations. Addition of glucagon during the activation results in a lowering of the Mg2+ requirement for full activation from 25 mM to around 10 muM and in concomitant increases in both the rate and the extent of N activation. In contrast to its dramatic effect on Mg2+ requirement, glucagon has little (less than 2-fold) effect on the GTP[gamma S] requirement of N activation. These experiments indicate that the glucagon receptor facilitates activation of N by: (i) decreasing the apparent Km of N for Mg2+, and (ii) increasing the extent of activation that can be elicited by saturating concentrations of guanine nucleotide. It is postulated that the mechanism by which Mg2+ and receptors facilitate N activation involves dissociation of n alpha activated ADP-ribosylatable subunits (with guanine nucleotide bound to them) from n beta non-ADP-ribosylatable subunits (with receptor and Mg2+ bound to them).
 ...
PMID:Hormone receptor modulates the regulatory component of adenylyl cyclase by reducing its requirement for Mg2+ and enhancing its extent of activation by guanine nucleotides. 629 Oct 28

Glucagon and 11 glucagon derivatives were characterized and compared with respect to the cooperativity of their receptor interactions and their ability to elicit a biphasic (activation-inhibition) response from the adenylate cyclase system of rat liver plasma membranes. Slope factors were evaluated from two sets of experimental data, binding to hepatocyte receptors and activation of adenylate cyclase. The results are consistent with noncooperative binding to a single affinity state of the glucagon receptor for all derivatives, irrespective of the modification and the agonist properties of the derivatives. High-dose inhibition of adenylate cyclase activity was observed for native glucagon and all of the derivatives which were examined at high concentrations (greater than 10(-5) M). Partial agonism of some low-affinity glucagon derivatives is not caused by high-dose inhibition. Several mechanisms which might give rise to high-dose inhibition such as receptor cross-linking or multivalent receptor binding are discussed in relationship to the glucagon-receptor interaction. These phenomena indicate that significant differences exist between the glucagon system and the beta-adrenergic system.
 ...
PMID:Noncooperative receptor interactions of glucagon and eleven analogues: inhibition of adenylate cyclase. 630 93

Specific labeling of liver plasma membrane glucagon receptors has been achieved by the photoincorporation of a 125I-labeled photoderivative of glucagon, NE-4-azidophenylamidinoglucagon. Identification of glucagon receptors was facilitated by irradiating membranes in the presence of excess unlabeled glucagon. Isoelectric focusing of radioiodinated membrane proteins revealed one major band of glucagon displaceable material which had an isoelectric point of 5.85. When this material was isolated and run on SDS-polyacrylamide gels a major labeled band of Mr55000 was obtained which had properties consistent with those of the glucagon receptor. These studies indicate that a purification of the glucagon receptor of greater than 700-fold can be attained through the use of isoelectric focusing and SDS-polyacrylamide electrophoresis.
 ...
PMID:Partial purification and characterization of the glucagon receptor. 630 43

For a variety of ligand states, adenylate cyclase activity in the presence of Mn2+ was greater than with Mg2+. Trypsin treatment of intact hepatocytes, under conditions which destroy cell surface glucagon receptors, led to a first order loss of glucagon-stimulated adenylate cyclase activity in isolated membranes assayed in the presence of Mn2+ whether or not GTP (100 microM) was present in the assays. Arrhenius plots of basal activity exhibited a break at around 22 degrees C, those with NaF were linear and those with glucagon +/- GTP (100 microM) were biphasic with a break at around 28 degrees C. It is suggested that Mn2+ perturbs the coupling interaction between the glucagon receptor and catalytic unit of adenylate cyclase at the level of the guanine nucleotide regulatory protein. This appears to take the form of Mn2+ preventing GTP from initiating glucagon's activation of adenylate cyclase through a collision coupling mechanism.
 ...
PMID:Mechanism of glucagon activation of adenylate cyclase in the presence of Mn2+. 630 47

The 29 amino acid polypeptide hormone glucagon was cleaved into two large fragments by the enzyme clostripain. The conformational properties of these two fragments were monitored by circular dichroism at pH 2 and 12 in both the presence and absence of sodium dodecyl sulfate. Both glucagon (1-17) and glucagon (19-29) have reduced abilities to fold in aqueous solution. However, both fragments can take on structure of higher apparent helical content in acidic solution in the presence of sodium dodecyl sulfate but only the glucagon (19-29) retains this conformation at high pH. Neither of the two fragments react with dimyristoylphosphatidylcholine as the intact peptide does. Only the carboxyl terminal fragment was capable of reacting with an antibody specific for glucagon. The glucagon (1-17) has markedly reduced affinity for binding to the glucagon receptor as well as markedly reduced ability to stimulate adenylate cyclase activity which is not affected by the presence of glucagon (19-29). It is proposed that the intact sequence provides specific groups required for activity as well as the potential for forming a stable amphipathic helix, both of which are necessary for full biological activity at low peptide concentrations.
 ...
PMID:Conformational and biological properties of glucagon fragments containing residues 1-17 and 19-29. 631 39

Glucagon receptor levels, glucagon-stimulated and other forms of adenylyl cyclase activity, and regulatory component activity of adenylyl cyclase were determined in hepatic plasma membranes of rats administered streptozotocin without and with insulin to produce varying degrees of hyperglycemia. Receptor levels were assayed by direct binding of the specific probe [125I-Tyr10]-iodoglucagon; regulatory component activity was assayed by the capacity to reconstitute stimulatory regulation in deficient membranes from cyc- S49 murine lymphoma cells. In rats given 150 mg streptozotocin, glucagon stimulation of adenylyl cyclase as well as basal, sodium fluoride, 5' guanylylimidodiphosphate [GMP-P(NH)P] and Mn-dependent activities were reduced 50%, glucagon receptor levels but not affinity were reduced 67%, and regulatory component activity was decreased 50%. In addition, alpha 1-adrenergic receptors and 5'-nucleotidase were similarly reduced in diabetes. However, specific ouabain-inhibitable Na+, K+, ATPase activity was not altered by streptozotocin treatment. The streptozotocin-induced changes were noted within 24 h and became maximal by 120 h after its administration. All of these decreases were partially reversed by in vivo insulin treatment. DNA, cytochrome c oxidase, glucose-6-phosphatase, and N-acetyl-beta-glucosaminidase content in hepatic plasma membrane preparations were not substantially different in diabetic as compared with control animals. The data demonstrate that glucagon-mediated regulation of cyclic AMP formation is deranged in insulin deficiency owing to a combined decrease in receptors, derangement of the coupling mechanism intervening between receptor and adenylyl cyclase, and possibly, an altered basal effector system. Some of these changes appear to reflect a "desensitization-like" phenomenon which may or may not be attributable to the hyperglucagonemia of diabetes mellitus. There also appears to be a concurrent generalized decrease in several but not all plasma membrane receptor and enzymatic proteins. This may be the result of a number of processes among which is the accelerated proteolysis of uncontrolled diabetes.
 ...
PMID:Glucagon-stimulable adenylyl cyclase in rat liver. The impact of streptozotocin-induced diabetes mellitus. 632 32


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>