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)

Alternate scan 13C and 31P NMR has been used to follow the metabolism of 13C-labeled substrates, in the presence and absence of insulin, in isolated perfused liver from fasted rats. Because both 31P and 13C NMR spectra are recorded almost simultaneously with this method, both phosphate metabolites and 13C-labeled metabolites are measured, noninvasively and repetitively, to give an immediate, broad survey of the hepatic response to a variety of stimuli. During the metabolism of [2-13C]pyruvate, [1,2-13C]ethanol, and NH4+, 13C-labeled glycogen increases synchronously with, and at the same rate as, the synthesis of 13C-labeled glucose; thus, glycogenesis was essentially a gluconeogenic process under our conditions and was unaltered by the presence of insulin. From the position of the 13C-labeled citrate peak observed in liver, the measurement of KD for the citrate-magnesium complex under our conditions, and the expression relating these quantities to the concentration of free Mg2+, the intracellular level of free Mg2+ is estimated to be 0.46 +/- 0.05 mM. Later administration of glucagon led to a rapid decrease in glycogen and citrate and a 44% increase in glycero-3-phosphocholine (GPC); increase in GPC is consistent with stimulation of liver phospholipase activity by glucagon. Simultaneous administration of two different 13C-labeled substrates, or one doubly labeled substrate, introduced multiplet structure arising from spin-spin interaction between labeled adjacent carbons into the peaks of several key metabolites. The 13C NMR intensity distributions within the several multiplets are used, within the context of a first-order model for fluxes into the Krebs cycle, to estimate relative fluxes under the conditions of the experiment.
 ...
PMID:Application of 13C and 31P NMR to the study of hepatic metabolism. 637 71

High-field 13C surface coil nuclear magnetic resonance has been employed to investigate glucose and glycogen metabolism in rat liver in vivo. Natural abundance and isotopically enriched proton-decoupled 13C NMR experiments were conducted at 90.56 MHz on a standard commercial spectrometer utilizing a laboratory-built high-sensitivity double-resonance coaxial coil probe. At variance with a previous preliminary report, natural abundance spectra of the liver in vivo from a rat fed ad libitum reveal resonances of substantial intensity from hepatic glycogen with approximately 10 min of signal averaging. The response of hepatic glycogen levels to an intravenous injection of the hormone glucagon was continuously monitored through the glycogen C-1 carbon resonance intensity; this revealed an average 60% depletion of hepatic glycogen stores in vivo within approximately 1 h. In a complementary study utilizing fasted rats, 100 mg of D-[1-13C]glucose (90% enriched) was administered via a peripheral vein injection and continuously monitored by 13C NMR with 3-min time resolution as it was incorporated into hepatic glycogen. The C-1 carbon resonances of hepatic glucose and glycogen are well-resolved in vivo enabling the time course for the relative change in concentration for both metabolites to be established simultaneously. The 13C label incorporated into the glycogen pool reaches a steady-state level in approximately 40 min.
 ...
PMID:Direct observation of glycogenesis and glucagon-stimulated glycogenolysis in the rat liver in vivo by high-field carbon-13 surface coil NMR. 650 Dec 76

A literature search on the structural aspects of glucagon in dilute aqueous solution has been undertaken. We have found that a compact, well-defined structure must exist and propose a model for that structure. In doing so, care was taken to distinguish between the raw data themselves and the interpretations drawn from them, and to bring about a model consistent with as much of the data as possible. The model building was performed on Corey-Pauling-Koltun (CPK) space-filling models using secondary structure prediction rules, experimental data such as fluorescence quenching, circular dichroism, NMR and high resolution dark field electron microscopy, and was guided by a hierarchy of intramolecular interactions which places hydrophobic bonding first and hydrogen bonding second. This last criterion places a strict requirement on the model-building to maximize contacts among complementary hydrophobic surfaces; this means that no empty spaces are allowed inside the folded molecule. The resultant model is consistent with all the relevant data. Furthermore, as demanded by any structure building exercise, the model suggests structure-function relationships. One of the predictions drawn from the structure--the binding of guanosine-5'-triphosphate (GTP)--has been confirmed by a preliminary experiment (reported elsewhere). Another aspect of the structure suggests a subtle mechanism for allostery.
 ...
PMID:A model for the three-dimensional structure of glucagon. 665 88

Natural-abundance 13C NMR signals from glycogen are observable in situ within the perfused livers of rats. The nuclear magnetic relaxation properties (T1, T2, eta + 1) of glycogen were measured for glycogen in situ and in vitro and were found to be identical. All of the carbon nuclei in glycogen contribute to the high-resolution NMR spectrum, in spite of glycogen's very large molecular weight. The metabolism of glycogen in situ in the perfused rat liver was followed by 13C NMR. Stimulation of the fed rat liver by physiological glucagon levels led to rapid glycogenolysis. Perfusion of the liver with [1-13C]glucose led to net glycolysis, with concomitant scrambling of the label from C1 to C6 due to triosephosphate isomerase activity.
 ...
PMID:Structure and metabolism of mammalian liver glycogen monitored by carbon-13 nuclear magnetic resonance. 683 41

The gluconeogenic pathway from 13C-labeled substrates, each of which contained the 14C-labeled counterpart at a tracer level, has been followed in isolated rat liver cells and in isolated perfused mouse liver. The gluconeogenic flux from glycerol, the synthesis of glycogen, the stimulation of glycogenolysis by glucagon, the recycling of triacylglycerol, and an increase in pentose cycle activity under the influence of phenazine methosulfate were all observed directly in the 13C NMR spectra of perfused liver or isolated hepatocytes. The relative concentrations of 13C label at specific carbons measured by the NMR spectra under these conditions agreed closely with 14C isotopic distributions measured in extracts of the same doubly labeled samples for specific activities of greater than or equal to 3%. The label distributions measured by both methods were the same to within the experimental errors, which ranged from +/- 2% to +/- 7% in these experiments.
 ...
PMID:A comparison of 13C nuclear magnetic resonance and 14C tracer studies of hepatic metabolism. 700 12

Fluorescence studies showed that glucagon binds to a variety of micellar lipids. By means of ultracentrifugation and quasi-elastic light-scattering, it was found that stoichiometrically well defined complexes were formed between glucagon and perdeuterated dodecylphosphocholine micelles consisting of one glucagon molecule and approx. 40 detergent molecules. Well resolved 1H-NMR spectra were obtained for glucagon in the deuterated micelles. Studies of nuclear Overhauser effects between individually assigned protons in different regions of the amino acid sequence indicated that micelle-bound glucagon adopts a well defined, predominantly extended conformation. Evidence obtained from circular dichroism indicates that the conformation of glucagon bound to various micellar lipids is largely independent of the type of lipid and, furthermore, appears to be very similar to that of glucagon bound to lipid bilayers.
 ...
PMID:Physicochemical characterization of glucagon-containing lipid micelles. 745 56

Somatostatin is a hypothalamic hormone that inhibits the release of growth hormone (GH). It has also been shown to inhibit the release of a broad range of hormones including insulin, glucagon, and gastrin. Presently, five different receptor subtypes of somatostatin have been characterized and cloned. Our previous work on the structure-activity relationship of somatostatin and that of many others has generated a large database of analogues with different biological activities and receptor affinities. This present work is an investigation of the growth hormone release-inhibiting potencies of somatostatin analogues by the three-dimensional quantitative structure-activity paradigm, comparative molecular field analysis (CoMFA). A total of 64 analogues were modeled in SYBYL using structural information from two NMR studies. The molecules were aligned by a root-mean-square fit of atoms and field-fit of the steric and electrostatic molecular fields and the resulting databases analyzed by partial least squares analysis with cross-validation to extract the optimum number of components. The analysis was then repeated without cross-validation to give the final QSAR models. Preliminary investigations with the CoMFA models led to the synthesis of a new somatostatin analogue. This compound together with five other newly synthesized compounds not included in the original training sets were used to test the predictive ability of the CoMFA models. Two models with good predictive powers are presented.
 ...
PMID:Three-dimensional quantitative structure-activity relationships of somatostatin analogues. 1. Comparative molecular field analysis of growth hormone release-inhibiting potencies. 778 29

We have used 2D 1H NMR to determine the structure of glucagon-like peptide-1-(7-36) amide bound to a dodecylphosphocholine micelle. In this membranelike environment, the peptide hormone is shown to have a structure similar to that observed for glucagon. It consists of an N-terminal random coil segment (residues 1-7), two helical segments (7-14 and 18-29), and a linker region (15-17). The C-terminal helix is more stable than the N-helix as determined by amide proton exchange experiments. The C-terminal helix shows much larger alpha and amide proton upfield secondary shifts relative expected for a random coil conformation. This suggests a highly helical structure in this portion of the molecule. The C-terminal helix also has a much larger fraction of residues that are hydrophobic, presumably enhancing the interaction of this portion of the peptide with the micelle (or membrane). The structure refined from the NOESY data is not a uniform alpha-helix throughout residues 6-30. A uniform helix would not be perfectly amphiphilic since the hydrophobic face of the N-terminal portion of the helix is positioned in nearly perfect opposition to the hydrophobic face of the C-terminal portion. However, helical distortion around residues 15-17 allows a phase shift of the two helical segments to position nearly all of the hydrophobic residues (and none of the hydrophilic ones) on a single face of the distorted single helix as would be required to favorably interact with the hydrophobic portion of the micelle or membrane.
 ...
PMID:Structure of glucagon-like peptide (7-36) amide in a dodecylphosphocholine micelle as determined by 2D NMR. 814 50

The rate of glycogenolysis was measured using 13C-NMR in vivo in the rat heart following a glucagon bolus. Glycogen that had just been synthesized during a 50 min infusion of D-[1-13C]glucose and insulin was degraded at a rate of 2.5 mumol/min/g wet wt following a 250 micrograms bolus of glucagon. If a second 50 min infusion of unlabelled glucose followed the D-[-13C]glucose, the rate of mobilization of the labelled glycogen following glucagon was slower (0.52 mumol/min/g wet wt), indicating that the labeled glycogen was less accessible to the activated phosphorylase. Glycogen phosphorylase a (GPa) activity was measured in hearts freeze-clamped at intervals after the glucagon bolus. Activity rose rapidly to 6-fold basal and then returned to basal over 20-30 min (t1/2 decay of phosphorylase activity = 5.1 min). This time course paralleled the exponential fall in heart glycogen which followed glucagon (t1/2 = 4.3 min). Throughout the post-glucagon period the activity of phosphorylase exceeded the rate of glycogenolysis. These findings suggest that the activity of the phosphorylated form of glycogen phosphorylase (GPa) is an important but not the sole determinant of glycogen breakdown in the heart after a glucagon bolus.
 ...
PMID:The time course of myocardial glycogenolysis stimulated by glucagon. 847 25

The analysis of crude tissue extracts by NMR has proven to be of use in the study of metabolism due to the non-destructive and non-selective character of the technique. Lists of 1H and 31P NMR assignments of phosphorus metabolites in water solution at specified pH and ionic composition are of large general value but their usefulness may be limited when analysing complex mixtures of metabolites at low concentrations. In this work we report on the use of gradient-assisted proton detected multiple quantum 1H and 31P coherence experiments with selective pulses for the rapid and unambiguous assignments of some crowded regions in 1H and 31P spectra of crude extracts from rat liver. The amplitudes of the gradient episodes were calibrated to optimize the coherence transfer pathway between proton and phosphorus, and the delay for the evolution of the long-range coupling was calculated from values of 3JPH and 4JPH ranging from 1.4 to 7.5 Hz. Moreover, a selective 90 degrees Gaussian pulse on the 31P channel was introduced to increase the resolution in the F1-domain and make the method even faster. The procedure was then applied to unambiguously assign the ID 31P and 1H spectra of perchloric acid extracts of rat livers that had been stimulated with phenylephrine, dBcAMP and glucagon and thus detect changes in the concentration of less abundant metabolites such as phosphoenolpyruvate, UDP-glucose and AMP. The fact that the quantification of these metabolites by either 31P and 1H methods lead to different results is discussed, and the use of 1H NMR spectroscopy for the quantification of phosphorus metabolites whose signal are too weak or poorly resolved in a 31P spectrum is proposed.
NMR Biomed 1995 Aug
PMID:Detection and quantitation of phosphorus metabolites in crude tissue extracts by 1H and 31P NMR: use of gradient assisted 1H-31P HMQC experiments, with selective pulses, for the assignment of less abundant metabolites. 866 4


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