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)

Some effects of salts on the adenylate cyclase of partially purified plasma membranes from rat liver have been studied. Under conditions where cyclic adenosine 3':5'-monophosphate formation was linear with respect to time and protein concentration, the enzyme was stimulated 3- to 6-fold by 10 mM NaF, 10- to 30-fold by 1 muM glucagon, 4- to 5-fold by 0.1 mM 5'-guanylylimidodiphosphate, and in the presence of 3 muM GTP, 2-fold by 10 mug/ml of prostaglandin E1. Various salts were found to stimulate basal activity slightly, but enhanced the response to NaF 3- to 4-fold, to glucagon 1.5- to 2-fold, to 5'-guanylylimidodiphosphate 2- to 3-fold, and to prostaglandin E1 1.5-fold. This enhancement was observed at maximally effective concentrations of each of the respective activators. Of the salts tested, NaN3 and the Na- or K-halides were most effective. Their action appeared to be due to the respective anions. Stimulation was detectable with 1.5 mM NaN3 or 3 mM NaCl and was maximal with 30 mM NaN3 or 60 mM NaCl. The stimulatory effect of NaN3 was not due to ATP-sparing, nor to an altered cyclic adenosine 3':5'-monophosphate recovery. It was independent of the chromatography and assay methods used, and was therefore not due to procedural artifact. Fluoride-stimulated cyclase activity was enhanced by salts to a greater degree than were 5'-guanylylimidodiphosphate-, glucagon-, or (prostaglandin E1 + GTP)-stimulated activities. The effects of NaN3 were not the result of significant changes in the enzyme's responses to GTP, which increased basal and glucagon-stimulated activities but inhibited F--stimulated activity. The effects of NaN3 were greater when cyclase was assayed with Mn2+ than with Mg2+. The facilitatory effect of NaN3 or NaCl on fluoride-stimulated adenylate cyclase activity was partially reversible as was the stimulatory effect of fluoride in the presence of NaN3. Enhancement of hormonal stimulation by NaN3 was also demonstrable with cardiac and adipose tissue adenylate cyclase. However, NaN3 did not stimulate detergent-dispersed adenylate cyclases from either liver plasma membranes or brain. The data suggest that stimulation of adenylate cyclase by salts may require the added presence of other stimulatory agents and an intact membrane structure.
 ...
PMID:Liver membrane adenylate cyclase. Synergistic effects of anions on fluoride, glucagon, and guanyl nucleotide stimulation. 12 55

The present study was initiated to determine whether specific hormones would influence adenylate cyclase activity within the maxillary-palatal complex during formation of the hamster secondary palate. Stages from initial appearance of the palatal processes to shortly after birth were studied. Highest basal adenylate cyclase activities occurred during the earliest periods of palate development. This basal enzyme activity began to diminish as palatal fusion occurred and remained lowered until birth. Activation of adenylate cyclase by fluoride was maximal at concentrations of 5-10 mM, and was observed throughout the span of palatal development. Fluoride activation of adenylate cyclase was greatest prior to fusion of the palatal processes, then decreased until birth when a slightly increased enzymatic stimulation was seen. Norepinephrine and epinphrine were the catecholamines most capable of inducing increased activation of adenylate cyclase at most periods of palatal growth. Increased enzyme activity in the presence of norepinephrine was more susceptible to antagonism by the beta adrenergic agent, propranolol, than to the alpha adrenergic agent, phentolamine. The remaining catecholamines, namely isoproterenol and dopamine, displayed a lesser ability to activate the enzyme, and adenylate cyclase was not equally responsive to these catecholamines at identical developmental stages. Other hormones, i.e. histamine, serotonin, thyrotropin, growth hormone, thyroxine and glucagon were generally ineffective in activating the enzyme. Phosphodiesterase activity was not detected until shortly before birth.
 ...
PMID:Catecholamine-sensitive adenylate cyclase in the developing golden hamster palate. 17 49

Plasma membranes were prepared from homogenates of two well differentiated hepatomas (Morris rat 7787 and Dalton mouse 9815), two poorly differentiated hepatomas (Morris rat 7288-C and Dalton mouse 129), and normal liver. Adenylate cyclase activity and [125I]iodoglucagon binding were measured in the plasma membrane preparations over a wide range of glucagon concentrations. Nether glucagon-stimulated adenylate cyclase activity nor [125I]iodoglucagon binding could be detected in the poorly differentiated hepatomas. Fluoride and epinephrine stimulated adenylate cyclase activity in all hepatomas. Maximum activity of glucagon-stimulated adenylate cyclase and maximum binding of glucagon in the wall differentiated hepatomas were less than those of normal liver. Plasma membranes from liver and hepatomas were solubilized with Lubrol-PX and, after reducing the concentration of detergent, were incubated with [125I]iodoglucagon and then chromatographed on a column of Bio-Gel A 1,5 m. Two peaks containing both protein and [125I]iodoglucagon were found for normal liver but not for the poorly differentiated hepatomas. Fractions from the Bio-Gel column containing the greatest concentration of protein were also subjected to a binding microassay. Material from the poorly differentiated tumors did not bind glucagon in this system, whereas the solubilized normal liver membranes bound up to 1.4 pmol [125I]iodoglucagon/mg protein. This indicates that there is no detectable glucagon receptor in these undifferentiated tumors.
 ...
PMID:Membrane receptor function and the loss of glucagon-stimulated adenylate cyclase activity in hepatomas. 21 18

The effect of 10 mM fluoride on glycerol production in vitro from rat epididymal adipocytes was investigated. Fluoride had no effect on the basal glycerol production, irrespective of the presence or absence of Ca++ and Mg++ ions. When stimulating the glycerol production with 10 mM theophylline, fluoride reduced the stimulation in the absence of either Ca++ or Mg++ or both. In the presence of both ions, fluoride had no effect on the theophylline stimulation. Fluoride also reduced the stimulative effect of adrenaline on glycerol production, but not that of glucagon. Increased adrenaline concentration could not overcome the inhibitory effect of fluoride.
 ...
PMID:Effect of fluoride on glycerol production in rat adipocytes in vitro. 57 58

Stimulated and basal adenylate cyclase activities from livers of young and old rats were lower in particulates than in homogenates. Particulates were compared to homogenates by reconstituting the suspensions to the volume of the homogenates from which they were derived; enzyme activities in paired homogenates and particulates therefore reflected the same amounts of membrane-bound enzyme. The magnitude of the losses of hormone-sensitive activities in particulates was dependent on the age and sex of the animals and the concentrations of hormone. Particulates from 3-month-old animals showed glucagon-(1 . 10(-5) M) and epinephrine-sensitive (1 . 10(-4) M) activities which were 67 and 78% of homogenate activities, respectively; particulates from 24-month-old animals had activities relative to homogenates of 55% for glucagon and as low as 32% for epinephrine. The glucagon dose vs. response curve in particulates and membranes showed maximal activity at 1 . 10(-7) M glucagon while in homogenates activity increased linearly with increasing glucagon concentrations up to 1 . 10(-5) M. Losses of basal and anion-stimulated activities were similar at both ages. Fluoride and azide stimulations relative to basal activities were greater in particulates than in homogenates, while relative epinephrine activity was lower in particulates, suggesting qualitative alteration of adenylate cyclase during preparation of particulates. These studies show that adenylate cyclase activity in rat liver is presently best quantitated in homogenates and suggest caution in comparisons of enzyme activities based on particulates or membranes prepared from animals of differing physiologic states.
 ...
PMID:Quantitation of epinephrine- and glucagon-sensitive adenylate cyclases of rat liver. Implications of alterations of enzymatic activities during preparation of particulate fractions and membranes. 65 70

Adenylate cyclase activity in liver, lung, pancreas, and heart ventricle, from full-term and premature newborns has been assayed. Of all tissues studied, heart had the highest activity. Fluoride 10 mM stimulates adenylate cyclase in all tissues. Glucagon evoked a small activation of liver adenylate cyclase.
 ...
PMID:Adenylate cyclase activity in human tissues. 97 87

Isolated rat hepatocytes were used to investigate the possibility of a short-term effect of glucagon on the synthesis of triacylglycerols in the liver. Incubation of hepatocytes in the presence of glucagon, followed by homogenization in a buffer containing F- (50 mM) and EDTA (2.5 mM), resulted in a 53% decrease in activity of microsomal diacylglycerol acyltransferase (EC 2.3.1.20), the only enzyme that is exclusively involved in the synthesis of triacylglycerols. The activity of cholinephosphotransferase (EC 2.7.8.2), which also uses diacylglycerols as substrate, was not decreased after exposure of the hepatocytes to glucagon. This may imply that triacylglycerol synthesis can be regulated independently of phosphatidylcholine synthesis. The activity of diacylglycerol acyltransferase in microsomes isolated from a homogenate of whole liver could be reduced by preincubating the microsomes with Mg2+ (5 mM), ATP (1 mM) and 105 000 X g supernatant. The enzyme could be reactivated by incubation of the washed microsomes with a 105 000 X g supernatant in the presence of dithiothreitol (5 mM). Fluoride (50 mM) inhibited this reactivation. It is concluded that the activity of diacylglycerol acyltransferase is subject to hormonal short-term control, possibly via a phosphorylation-dephosphorylation mechanism.
 ...
PMID:Regulation of triacylglycerol synthesis in the liver: a decrease in diacylglycerol acyltransferase activity after treatment of isolated rat hepatocytes with glucagon. 626 42

Ca2+ decreased the lipid fluidity of rat liver plasma membranes labeled with 5-nitroxide stearate, I(12,3), as indicated by the order parameter (S). These effects form a reversible, saturable process with an association constant of 1 x 10(3) M-1. Arrhenius-type plots of S indicated that the lipid phase separation, present in the external leaflet of native membranes between 28 and 19 degrees C, is perturbed by mM Ca2+ such that the high temperature onset is elevated to 32-34 degrees C. Fluoride-stimulated adenylate cyclase was similarly inhibited by Ca2+ (ID50 = 1 mM) for the enzyme in membrane-bound or solubilized states. The glucagon-stimulated activity was more sensitive to Ca2+ inhibition with an ID50 of 0.2 mM. These inhibitory effects are due neither to perturbations of glucagon binding to its receptor nor to fluidity changes, but are instead attributed to direct Ca2+-enzyme interactions. Such binding desensitizes the enzyme to fluidity alterations induced by temperature elevation or benzyl alcohol addition. With Ca2+, Arrhenius plots of glucagon-stimulated activity indicated breaks at 32 and 16 degrees C, whereas those of fluoride-stimulated activity showed one break at 17 degrees C. Without Ca2+, Arrhenius plots exhibited one break at 28 degrees C for glucagon-stimulated activity, whereas fluoride-stimulated plots were linear. We propose that Ca2+ achieves these effects through asymmetric perturbations of the membrane lipid structure.
 ...
PMID:Perturbations of liver plasma membranes induced by Ca2+ are detected using a fatty acid spin label and adenylate cyclase as membrane probes. 629 44

Isolated hepatocytes converted exogenous [alpha-32P]ATP to cyclic [32P]AMP at high rates. This system was used for kinetic studies of the effects of glucagon, fluoride, free magnesium and free ATP4- on adenylate cyclase. In the absence or presence of glucagon, free Mg2+ activated adenylate cyclase by decreasing the Km for MgATP2- without changing V. Free ATP4- was not a potent inhibitor of adenylate cyclase and the only effect of glucagon was to increase V. Fluoride also increased the V of adenylate cyclase, but, in contrast to the results obtained with glucagon, the effect increased as the concentration of free Mg2+ increased. One explanation of the effect of fluoride, consistent with the idea that free Mg2+ activates adenylate cyclase and free ATP is not an inhibitor, is that fluoride increases the affinity of the enzyme for Mg2+. Weak inhibition of adenylate cyclase by ATP4- in the presence of fluoride cannot be excluded.
 ...
PMID:The adenylate cyclase activity of isolated hepatocytes actions of glucagon and sodium fluoride. 739 47

Several lines of evidence indicate that glycolysis is especially important for normal diastolic relaxation and for the maintenance of cellular ion homeostasis in myocardium. To elucidate whether the glycolytic flux of ATP contributes to diastolic tone and to the regulation of intracellular Ca2+, myocardial content of sugar phosphates ([SP]) and intracellular Ca2+ concentration ([Ca2+]i) were measured in isolated, perfused ferret hearts using nuclear magnetic resonance. Glucose and acetate were used as substrates for glycolysis and oxidative phosphorylation, respectively. Glycogen was effectively depleted after 15-min perfusion with glucagon (2 mg/liter), as verified by the lack of rise in [SP] during exposure to iodoacetate (100 microM) in substrate-free perfusate. Despite the fact that glycolytic flux had been blocked both by iodoacetate and by absence of substrate, end-diastolic left ventricular pressure (EDP) remained unchanged (P > 0.15, n = 6). The subsequent addition of glucose to the perfusate led to SP accumulation and a marked rise in EDP, with a significant correlation between EDP and [SP] (r = 0.86 +/- 0.04, P < 0.01, n = 6). A similar correlation was observed when glucose in the perfusate was replaced by 2-deoxyglucose (r = 0.78 +/- 0.09, P < 0.01, n = 3). Fluorine nuclear magnetic resonance measurements of [Ca2+]i verified that EDP faithfully reports changes in diastolic [Ca2+]i under the present experimental conditions. Thus, intracellular Ca2+ overload is caused by the accumulation of SP rather than by the inhibition of glycolysis per se. Glycolysis may appear to be important because its by-products are deleterious, and not necessarily because glycolytically derived ATP plays a favored role in ion homeostasis.
 ...
PMID:Mechanism of the diastolic dysfunction induced by glycolytic inhibition. Does adenosine triphosphate derived from glycolysis play a favored role in cellular Ca2+ homeostasis in ferret myocardium? 813 61


1 2 Next >>