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 acid saline extract (ASE) of rat submaxillary gland exerts a powerful degrading effect on 125I-glucagon. In order to study the degradation of other 125I-peptides by ASE and the effects of their inhibitors, 125I-pancreatic polypeptide (PP) and 125I-insulin were used together with 125I-glucagon. The degradation studies were done by the trichloroacetic acid (TCA) method or gel filtration. Besides 125I-glucagon, 125I-PP was found to be destroyed by ASE in the ordinary immunoassay system using the TCA method, but 125I-insulin was intact in the presence of ASE. Leupeptin, and to a lesser extent p-chloromercuriphenyl-sulfonic acid (PCMS) and N-ethylmaleimide, inhibited the destruction of 125I-glucagon or -PP under the TCA method. PCMS was especially protective at high concentrations, for example 16 mM. These findings were confirmed by gel filtration of the assay mixture. In the presence of leupeptin (0.4 mM) and PCMS (16 mM), no shift in the peak of labelled glucagon or PP occurred. Thus ASE degrades not only 125I-glucagon but -PP, and thiol proteinase inhibitors have a strong inhibitory action on them.
 ...
PMID:Degradation of 125I-glucagon, -pancreatic polypeptide and -insulin by acid saline extract of rat submaxillary gland and their protection by proteinase inhibitors. 254 48

Glucagon receptors have been identified and characterized in intermediate (Gi) and heavy (Gh) Golgi fractions from rat liver. At saturation, plasma membranes bound 3500 fmol of hormone/mg of membrane protein, while Gi and Gh bound 24 and 60 fmol of 125I-glucagon/mg of protein, respectively. Half-maximal saturation of binding to plasma membranes, Gi, and Gh occurred at approximately 4, 10, and 20 nM 125I-glucagon, respectively. Trichloroacetic acid precipitation of intact, but not degraded, glucagon was used to correct binding isotherms for hormone degradation. After such correction, half-maximal saturation of binding to plasma membranes, Gi, and Gh was observed in the presence of approximately 2, 7, and 14 nM hormone, respectively. After 90 min of dissociation in the absence of guanosine 5'-triphosphate (GTP), 86% of 125I-glucagon remained bound to plasma membranes, whereas only 42% remained bound to Golgi membranes. GTP significantly increased the fraction of 125I-glucagon released from plasma membranes but only slightly augmented the dissociation of hormone from Golgi fractions. 125I-Glucagon/receptor complexes solubilized from plasma membranes fractionated by gel filtration as high molecular weight (Kav = 0.16), GTP-sensitive complexes and lower molecular weight (Kav = 0.46), GTP-insensitive complexes. 125I-Glucagon complexes solubilized from Golgi membranes fractionated almost exclusively as the lower molecular weight species. The lower affinity of Golgi than plasma membrane receptors for hormone, the ability of glucagon to stimulate plasma membrane, but not Golgi membrane, adenylyl cyclase, and the near absence of high molecular weight, GTP-sensitive complexes in solubilized Golgi membranes demonstrate that plasma membrane contamination of Golgi fractions cannot account for the 125I-glucagon binding.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Characterization of glucagon receptors in Golgi fractions of rat liver: evidence for receptors that are uncoupled from adenylyl cyclase. 301 9

Protein degradation in Reuber H35 hepatoma monolayers was measured as release of radioactive trichloroacetic acid-soluble material from intracellular protein labelled with [3H]leucine for 16 hr followed by 3-hr chase period. Proteolysis in this system was stimulated by physiological concentration of glucagon reaching a maximum at 10(-7) M with an increase of 30%. Dibutyryl cyclic AMP also had a stimulatory effect. When both glucagon and dibutyryl cyclic AMP were present at optimal concentrations, their effects were not additive suggesting that glucagon may act via the formation of cyclic AMP. In the presence of protein synthesis inhibitor, cycloheximide or puromycin, proteolysis remained responsive to glucagon. Glucagon counteracted the inhibitory effect of insulin on proteolysis.
 ...
PMID:Stimulation by glucagon and adenosine-3',5'-cyclic monophosphate of protein degradation in Reuber H35 hepatoma monolayers. 303 17

Cathepsin-D has been previously reported to cleave intact PTH into PTH-(1-34) and -(35-84) in membranous fractions of rat and bovine kidney. Whether PTH degradation occurs by intact kidney cells, however, has not been examined in detail. We have, therefore, examined this possibility using an opossum kidney (OK) cell line which possesses the characteristics of proximal renal tubules and responds to PTH. PTH radioimmunoreactivity recovered in trichloroacetic acid-soluble products and in fractions eluted from reverse phase HPLC was measured using an antibody directed to the midregion and C-terminus of PTH. In this study, intact OK cells, but not extracellular enzymes, cleaved human (h) PTH-(1-84) into three discrete fragments which were released into the medium in a time- and temperature-dependent fashion. Half-maximal velocity of PTH-degrading activity (PTHDA) was observed at 9 nM hPTH-(1-84). A 1000-fold molar excess of PTH antagonists [hPTH-(3-34) and [Tyr34]hPTH-(7-34)amide] markedly inhibited PTHDA, whereas ACTH, glucagon, or big gastrin did not suppress it, suggesting an involvement of the PTH receptor in PTHDA. This PTHDA was strongly inhibited by phenylmethylsulfonylfluoride and chymostatin, but not by trypsin inhibitor, elastatinal, or inhibitors of aspartic, cysteine, or metalloproteinases, suggesting that it is due to a seryl chymotrypsin-like endopeptidase. Analysis of chymotrypsin-digested products of hPTH-(1-84) eluted from HPLC exhibited five fragments detected by UV absorbance (210 nm), three of which were measurable by PTH RIA, and each corresponded to the three PTH fragments produced by OK cells. All three fragments were predominantly suppressed in the presence of chymostatin, suggesting that chymotrypsin-like activity is solely responsible for PTHDA in intact OK cells. To further explore the cleavage sites of PTH by chymotrypsin, amino acid analysis of chymotrypsin-cleaved products was performed. The results strongly support the conclusion that a chymotrypsin-like enzyme in OK cells cleaved the hormone between residues 23-24, and 34-35 to produce, at least, hPTH-(24-84) and -(35-84). Lysosomal blockers (chloroquine, ammonium chloride, or monensin) did not affect this PTHDA. Our present study indicates that chymotrypsin-like endopeptidase, but not other endopeptidase or lysosomal enzymes, is responsible for the limited hydrolysis of PTH by intact OK cells.
 ...
PMID:Parathyroid hormone degradation by chymotrypsin-like endopeptidase in the opossum kidney cell. 305 60

The occurrence of insulin receptors and biological responses to insulin has been investigated in trypsin-dissociated fetal rat brain cells maintained in culture for 8 days. Binding of [125I]insulin to brain cells in culture was time- and pH-dependent and 85--90% specific. Porcine insulin competed for [125I]insulin binding in a dose-dependent manner. Unrelated polypeptides, including angiotensin II, glucagon, bovine growth hormone, and bovine prolactin did not compete for [125I]insulin binding. The half-life of [125I]insulin dissociation from receptors at 24 degrees C was 15 min and a plot of In[B/Bo] vs time suggested two dissociated rate constants of 2.7 X 10(-4) sec-1 and 5.0 X 10(-5) sec-1. Scatchard analysis of the binding data gave a curvilinear plot which may indicate negative cooperativity or the occurrence of both high affinity (Ka = 2 X 10(11) M-1) and low affinity (Ka = 4 X 10(10) M-1) sites. Of the estimated total of 4.9 X 10(4) binding sites per cell, 28--30% appear to be high affinity sites. Incubation of cultures with insulin caused a time- and dose-dependent stimulation of [3H]thymidine and [3H]uridine incorporation into TCA-precipitable material. Maximum stimulation of thymidine incorporation (2--5-fold) occurred 11 h after incubation with 167 nM insulin. The same concentration of insulin caused a 2.2-fold increase in [3H]uridine incorporation in 2 h. These results indicate that cells cultured from rat brain contain specific insulin receptors capable of mediating effects of insulin on macromolecular synthesis in the central nervous system.
 ...
PMID:Binding of [125I]insulin to specific receptors and stimulation of nucleotide incorporation in cells cultured from rat brain. 615 64

1. Protein degradation in rat hepatocytes in stationary monolayer culture was measured as release of radioactive trichloroacetic acid-soluble material from intracellular proteins labelled with [3H]leucine. 2. Glucocorticoids, but not other steroids, stimulated protein breakdown in the hepatocyte monolayers. The effects observed were greater when the cells were preincubated with the hormones, indicating that the stimulation was not immediate. In addition, the stimulation by glucocorticoids persisted for up to 4 h after hormone removal. 3. Cycloheximide and the lysosomotropic agents leupeptin and ammonia effectively blocked glucocorticoid stimulation of protein degradation. 4. Insulin blocked dexamethasone stimulation when added at the same time as the steroid, but not when added 3 h later. 5. Stimulation of protein breakdown by dexamethasone was additive with that by glucagon or dibutyryl cyclic AMP, suggesting that its mechanism of action is different from that of the latter two agents. 6. Total activities of several lysosomal enzymes were unaffected under conditions where protein breakdown was stimulated by either glucagon or dexamethasone. 7. It is suggested that, whereas glucagon, dibutyryl cyclic AMP and insulin modulate protein breakdown in these cells via changes in autophagocytosis, the stimulation by glucocorticoids is exerted independently, perhaps by stimulating the synthesis of membrane proteins essential to the autophagic process.
 ...
PMID:Stimulation by glucocorticoids of protein degradation in hepatocyte monolayers. 627 54

Degradation of 125I-iodoglucagon by human mononuclear cell preparations including one containing 18%-27% monocytes, one consisting of 97% pure monocytes and one consisting of 98% lymphocytes was examined. Intact cells were incubated with 125I-iodoglucagon and degradation assessed by measuring an increase in trichloroacetic acid soluble products or in non-immunoprecipitable products. The preparation consisting of intact lymphocytes did not degrade glucagon. Glucagon was degraded by preparations containing monocytes and this degradation increased with time. No difference between monocyte degradation as measured by trichloroacetic acid or immunoprecipitation was found. Degradation by intact monocytes and by mononuclear homogenates increased sixfold from 4 degrees C to 37 degrees C. Subcellular fractionation demonstrated that the majority of the neutral glucagon degrading activity was in the 100,000 g supernatant (cytosol). Kinetic analyses gave Km values of 1.1 x 10(-5) mol/l, 7.5 x 10(-6) mol/l, and 1.2 x 10(-5) mol/l for glucagon degradation by intact mononuclear cells, homogenates, and cytosol, respectively. Inhibitor studies indicated a sulphydryl dependent enzyme was involved in glucagon degradation by both intact cells and cytosol. The monocyte appeared to be the cell responsible for degradation of glucagon by mononuclear cell preparations. The degradation of glucagon under physiological conditions by intact monocytes was mediated by a neutral proteolytic enzyme, primarily localized in the cytosol.
 ...
PMID:Glucagon degradation by human mononuclear cells. 631 4

We examined the relationship between PTH binding and stimulation of cAMP formation in a cell line derived from opossum kidney (OK). In the presence of isobutylmethylxanthine (1 mM) bovine PTH(1-34) [bPTH(1-34)] (244 nM) stimulated cAMP accumulation in confluent cultures up to 40-fold over basal; this response to PTH was stable for 35 passages. The concentration of bPTH(1-34) required to raise cell cAMP levels half-maximally was 5-12 nM. Binding of [125I]bPTH(1-34) to OK cells was saturable; Scatchard analysis of competitive binding data yielded a dissociation constant (KD) = 6 +/- 2 nM, with 1.0 pmol binding sites/mg cell protein. Under steady state binding conditions 89% of labeled PTH remained precipitable by 10% trichloroacetic acid, suggesting minimal metabolism of the hormone. The PTH antagonist (8Nle, 18Nle, 34Tyr)bPTH(3-34)amide competed for [125I]bPTH(1-34) binding sites and inhibited the action of bPTH(1-34) to raise cAMP levels. The intact PTH molecule, bPTH(1-84), and the weak agonist hPTH(1-34) synthesized by Brewer were both less potent than bPTH(1-34) (6 times and 30 times, respectively) with regard to binding and cAMP production. Calcitonin and arginine vasopressin did not bind to PTH receptors but raised cAMP levels in OK cell cultures 3- and 10-fold, respectively; neither glucagon nor ACTH(1-24) influenced PTH binding of cAMP in OK cells. Varying the extracellular calcium concentration in the medium bathing cells did not influence basal or PTH-stimulated cAMP generation. These data suggest that PTH receptors in OK cells are of high affinity, are selective for PTH, and are coupled to adenylate cyclase. This established epithelial cell line provides a model in which to study the mechanism of action of PTH in the kidney.
 ...
PMID:Parathyroid hormone receptors coupled to cyclic adenosine monophosphate formation in an established renal cell line. 632 Nov 47

Effects of insulin and glucagon on the incorporation of [14C]glycine into the protein of liver slices and the opercular muscle of the eel were studied in vitro. Addition of insulin (0.1 IU/ml) to the medium increased the radioactivity both of the trichloroacetic acid (TCA)-soluble fraction and of the protein of the opercular muscle, indicating an acceleration by the hormone both of entry of the amino acid into the tissue and of protein synthesis. Insulin also increased the incorporation of [14C]glycine into the liver protein, while a decrease in the radioactivity of the TCA-soluble fraction was observed. These findings suggest that the hormone accelerated protein synthesis at the expense of an intracellular amino acid pool. In contrast, glucagon (5 micrograms/ml) did not affect the radioactivity either of the TCA-soluble fraction or of protein for either the opercular muscle or the liver. Thus, the present results highlight the importance of insulin in the regulation of protein synthesis in the eel both in muscle and in liver.
 ...
PMID:Effects of insulin and glucagon on the incorporation of [14C]glycine into the protein of the liver and opercular muscle of the eel in vitro. 635 2

1. Recycling of metabolites between fructose 6-phosphate and triose phosphates has been investigated in isolated hepatocytes by the randomization of carbon between C((1)) and C((6)) of glucose formed from [1-(14)C]galactose. 2. Randomization of carbon atoms was regularly observed with hepatocytes isolated from fed rats and was then little influenced by the concentration of glucose in the incubation medium. It was decreased by about 50% in the presence of glucagon. 3. Randomization of carbon atoms by hepatocytes isolated from starved rats was barely detectable at physiological concentrations of glucose in the incubation medium, but was greatly increased with increasing glucose concentrations. It was nearly completely suppressed by glucagon. These large changes can be attributed to parallel variations in the activity of phosphofructokinase. 4. The main factors that appear to control the activity of phosphofructokinase under these experimental conditions are the concentration of fructose 6-phosphate, the concentration of fructose 1,6-bisphosphate and also the affinity of the enzyme for fructose 6-phosphate. 5. The affinity of phosphofructokinase for fructose 6-phosphate was diminished by incubation of the cells in the presence of glucagon and also by filtration of an extract of hepatocytes through Sephadex G-25 and by purification of the enzyme. When assayed at 0.25 or 0.5mm-fructose 6-phosphate, the activity of phosphofructokinase present in a liver Sephadex filtrate was increased by a low-molecular-weight effector, which could be isolated from a liver extract by ultrafiltration, gel filtration or heat treatment, but was rapidly destroyed in trichloroacetic acid, even in the cold. This effector appears to be a highly acid-labile phosphoric ester. Its concentration was greatly increased in hepatocytes incubated in the presence of glucose and was decreased in the presence of glucagon.
 ...
PMID:Control of the fructose-6-phosphate/fructose 1,6-bisphosphate cycle in isolated hepatocytes by glucose and glucagon. Role of a low-molecular-weight stimulator of phosphofructokinase. 645 88


<< Previous 1 2 3 4 Next >>