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Results: 431 to 438 of 438

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Activity of various metalloporphyrin protein complexes with microsomal heme oxygenase.
Schacter BA, Waterman MR
(1974) Life Sci 14: 47-53
MeSH Terms: Animals, Carbon Monoxide, Cobalt, Copper, Cyanides, Deuterium, Fluorides, Globins, Heme, Hemeproteins, Iron, Ligands, Male, Metalloproteins, Methemoglobin, Microsomes, Microsomes, Liver, Nickel, Oxygenases, Palladium, Porphyrins, Potassium, Rats, Spleen, Structure-Activity Relationship
Added February 12, 2015
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25 MeSH Terms
Effect of ligands on alkaline denaturation of fetal hemoglobin and isolated gamma subunits.
Painter TD, Waterman MR
(1973) Biochem Biophys Res Commun 55: 812-7
MeSH Terms: Carboxyhemoglobin, Chromatography, Ion Exchange, Electrophoresis, Disc, Female, Fetal Hemoglobin, Humans, Hydrogen-Ion Concentration, Iron, Kinetics, Ligands, Mercuribenzoates, Methemoglobin, Peptides, Pregnancy, Protein Denaturation, Spectrophotometry, Time Factors, Umbilical Cord
Added February 12, 2015
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18 MeSH Terms
Mutational analysis of ligand binding activity of beta 2 adrenergic receptor expressed in Escherichia coli.
Breyer RM, Strosberg AD, Guillet JG
(1990) EMBO J 9: 2679-84
MeSH Terms: Amino Acid Sequence, Escherichia coli, Humans, Iodocyanopindolol, Kinetics, Ligands, Molecular Sequence Data, Mutation, Oligonucleotide Probes, Pindolol, Plasmids, Receptors, Adrenergic, beta, Recombinant Proteins, Restriction Mapping
Show Abstract · Added December 21, 2013
A novel in situ screening procedure was used to identify neutral mutations in the human beta 2 adrenergic receptor (beta 2AR). The coding region of the human beta 2AR gene was subcloned under transcriptional control of an inducible T7 promoter and used to transform Escherichia coli. Colonies expressing the beta 2AR bound the radiolabeled antagonist [125I]iodocyanopindolol and could be identified by autoradiography after transfer to nitrocellulose filters. The region of the beta 2AR between residues 76 and 83, in the second transmembrane helix, was mutagenized by a saturation mutagenesis technique, so that virtually all of the beta 2AR genes contained at least one mutation. Colonies retaining ligand binding activity were isolated using the in situ screen. Sequence analysis of the active mutant receptor genes allowed the identification of individual amino acid side chains which are essential for either ligand binding or structural integrity of the beta 2AR receptor.
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14 MeSH Terms
NMR methods for determining the structures of enzyme/inhibitor complexes as an aid in drug design.
Fesik SW, Zuiderweg ER, Olejniczak ET, Gampe RT
(1990) Biochem Pharmacol 40: 161-7
MeSH Terms: Drug Design, Enzyme Inhibitors, Ligands, Magnetic Resonance Spectroscopy, Pepsin A
Show Abstract · Added March 5, 2014
Four approaches are described for providing detailed structural information on large enzyme/inhibitor complexes to aid in the design of improved enzyme inhibitors. In one approach, proton NMR spectra are simplified by isotope-editing procedures in which only those protons that are attached to isotopically labeled nuclei (e.g. 13C or 15N) and their scalar or dipolar coupled partners are observed. Using this strategy, the conformation of an inhibitor bound to porcine pepsin can be determined and structural information on the active site obtained. In another approach, two-dimensional nuclear Overhauser effect (2D NOE) difference spectra are obtained by subtracting NOE spectra of two enzyme/inhibitor complexes prepared with either a protonated or a deuterated inhibitor. Only NOEs arising from protons of the inhibitor substituted with deuterium appear in the 2D NOE difference spectra as illustrated for a pepsin/inhibitor complex. In a third strategy, deuterated enzymes are employed to eliminate the many proton NMR signals of the enzyme and allow the selective detection of the resonances corresponding to the bound ligand as demonstrated for CTP bound to CMP-3-deoxy D-manno-octulosonic acid (KDO) synthetase. Finally, a fourth approach is described using heteronuclear three-dimensional NMR spectroscopy in which homonuclear 2D NMR spectra are edited with respect to the heteronuclear chemical shifts. Using these methods the complete three-dimensional structures of large enzyme/inhibitor complexes can potentially be obtained. Examples of the spectral simplification that can be achieved using 3D NMR are given for 15N-labeled CMP-KDO synthetase complexed with an inhibitor and CTP.
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5 MeSH Terms
Opioid signal transduction in intact and fragmented SH-SY5Y neural cells.
Carter BD, Medzihradsky F
(1992) J Neurochem 58: 1611-9
MeSH Terms: Endorphins, Enkephalin, Ala(2)-MePhe(4)-Gly(5)-, Enkephalins, Guanosine Triphosphate, Humans, Intracellular Membranes, Ligands, Nervous System Neoplasms, Signal Transduction, Tumor Cells, Cultured
Show Abstract · Added March 5, 2014
Parameters of ligand binding, stimulation of low-Km GTPase, and inhibition of adenylate cyclase were determined in intact human neuroblastoma SH-SY5Y cells and in their isolated membranes, both suspended in identical physiological buffer medium. In cells, the mu-selective opioid agonist [3H]Tyr-D-Ala-Gly(Me)Phe-Gly-ol ([3H]DAMGO) bound to two populations of sites with KD values of 3.9 and 160 nM, with less than 10% of the sites in the high-affinity state. Both sites were also detected at 4 degrees C and were displaced by various opioids, including quaternary naltrexone. The opioid antagonist [3H]naltrexone bound to a single population of sites, and in cells treated with pertussis toxin the biphasic displacement of [3H]naltrexone by DAMGO became monophasic with only low-affinity binding present. The toxin specifically reduced high-affinity agonist binding but had no effect on the binding of [3H]naltrexone. In isolated membranes, both agonist and antagonist bound to a single population of receptor sites with affinities similar to that of the high-affinity binding component in cells. Addition of GTP to membranes reduced the Bmax for [3H]DAMGO by 87% and induced a linear ligand binding component; a low-affinity binding site, however, could not be saturated. Compared with results obtained with membranes suspended in Tris buffer, agonist binding, including both receptor density and affinity, in the physiological medium was attenuated. The results suggest that high-affinity opioid agonist binding represents the ligand-receptor-guanine nucleotide binding protein (G protein) complex present in cells at low density due to modulation by endogenous GTP.(ABSTRACT TRUNCATED AT 250 WORDS)
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10 MeSH Terms
Functional expression of the human serotonin 5-HT1A receptor in Escherichia coli. Ligand binding properties and interaction with recombinant G protein alpha-subunits.
Bertin B, Freissmuth M, Breyer RM, Sch├╝tz W, Strosberg AD, Marullo S
(1992) J Biol Chem 267: 8200-6
MeSH Terms: 8-Hydroxy-2-(di-n-propylamino)tetralin, Amino Acid Sequence, Binding, Competitive, Electrophoresis, Polyacrylamide Gel, Escherichia coli, GTP-Binding Proteins, Gene Expression, Guanosine 5'-O-(3-Thiotriphosphate), Humans, Ligands, Molecular Sequence Data, Plasmids, Receptors, Serotonin, Recombinant Proteins, Signal Transduction, Tetrahydronaphthalenes
Show Abstract · Added December 21, 2013
Signaling through serotonin 5-HT1A receptors involves multiple pathways. We have investigated the functional coupling of the human 5-HT1A receptor to different G proteins using an in vitro reconstitution system based on the expression of recombinant receptor (r5-HT1A) and G alpha-subunits (rG alpha) in Escherichia coli. The r5-HT1A receptor was expressed by insertion in a vector allowing its active expression in E. coli inner membranes. Binding of the selective agonist [3H] +/- 8-hydroxy-(2-N-dipropylamine)tetralin ([3H]8-OH-DPAT) to intact bacteria or E. coli membranes was saturable with a KD of approximately 8 nM and an average of 120 sites/bacterium. Binding properties of several serotoninergic ligands to r5-HT1A receptors were comparable with those measured in mammalian cells. Incubation of rG alpha.beta gamma with E. coli membranes resulted in high affinity agonist [3H]8-OH-DPAT binding (KD = 0.7 nM) and titration with a panel of rG alpha subtypes showed the order of potency: rGi alpha-3 greater than rGi alpha-2 greater than rGi alpha-1 much greater than rGo alpha, while rGs alpha appeared incapable of interacting with 5-HT1A receptors. Moreover, agonist-mediated enhancement of [35S]guanosine 5'-O-(3-thiotriphosphate) binding to rGi alpha confirmed the achievement of the functional interaction between receptor and G proteins. Our findings are in agreement with the in vivo ability of 5-HT1A receptors to activate Gi alpha related to adenylyl cyclase inhibition or K+ channel activation, but do not support previously reported adenylyl cyclase stimulation through interaction with Gs alpha.
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16 MeSH Terms
Conformation of two non-immunosuppressive FK506 analogs when bound to FKBP by isotope-filtered NMR.
Petros AM, Kawai M, Luly JR, Fesik SW
(1992) FEBS Lett 308: 309-14
MeSH Terms: Binding Sites, Calcineurin, Calmodulin-Binding Proteins, Carbon Isotopes, Carrier Proteins, Ligands, Magnetic Resonance Spectroscopy, Models, Molecular, Molecular Conformation, Phosphoprotein Phosphatases, Protons, Tacrolimus, Tacrolimus Binding Proteins
Show Abstract · Added March 5, 2014
The 3D structure of two unlabeled FK506 analogs, (R)- and (S)-[18-OH]ascomycin, when bound to [U-13C,15N]FKBP were determined by isotope-filtered 2D NMR experiments. The structures for the R and S isomers that bind tightly to FKBP but lack immunosuppressive activity are compared to each other and to the conformation of the potent immunosuppressant, ascomycin, when bound to FKBP. The results are interpreted in terms of calcineurin binding to the FKBP/ascomycin complex.
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13 MeSH Terms
Phosphofructokinase. II. Role of ligands in pH-dependent structural changes of the rabbit muscle enzyme.
Bock PE, Frieden C
(1976) J Biol Chem 251: 5637-43
MeSH Terms: Adenosine Triphosphate, Animals, Binding Sites, Enzyme Activation, Hydrogen-Ion Concentration, Inosine Nucleotides, Kinetics, Ligands, Magnesium, Muscles, Phosphofructokinase-1, Protein Binding, Protein Conformation, Rabbits
Show Abstract · Added January 20, 2015
The effect of ligands, including substrates and allosteric effectors, on the pH-dependent inactivation and reactivation of rabbit muscle phosphofructokinase has been examined in terms of the mechanism proposed previously (Bock, P.E. and Fireden, C. (1976) J. Biol. Chem. 251, 5630-5636). It is concluded thatt many ligands exert their effect by binding preferentially to either protonated or unprotonated forms of the enzyme and thus shifting an apparent pK for the inactivation or reactivation process. ATP and fructose 6-phosphate influence the apparent pK to different extents and in different directions, with ATP binding preferentially to the protonated forms and fructose 6-phosphate to the unprotonated forms. Enzyme inactivated by ATP can be reactivated by the addition of fructose 6-phosphate. The experiments indicate that inactivation and reactivation in the presence of these ligands can occur by kinetically different pathways as has been found for these processes in the absence of ligands. The results are discussed in relation to what might be expected for ligand binding properties of the enzyme as a function of pH, temperature, and enzyme concentration. The effect of ATP and MgATP is complex, perhaps representing more than one site of binding. Citrate appears to bind preferentially to protonated forms of the enzyme while fructose 1,6-bisphosphate and AMP bind preferentially to the unprotonated forms. ADP, K+, and NH4+ appear to have little or no preference in binding to different enzyme forms.
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14 MeSH Terms