Closure to “Discussion of ‘On the Differential Thermal Analysis of the Platinum‐Oxygen System’ [J. P. Hoare, R. F. Paluch, and S. G. Meibuhr (pp. 1821–1824, Vol. 123, No. 12)]”

Hoare, James P.; Paluch, Robert F.; Meibuhr, Stuart G.

doi:10.1149/1.2133444

Cited by 6 publications

(17 citation statements)

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“…3B. The K d value derived from this analysis was in excellent agreement with values derived using assay conditions defined to avoid artifacts (23,31,41) The B max of the radioligand was unaffected by haloperidol, as seen in Fig. 3A.…”

Section: Discussionsupporting

confidence: 71%

“…The present data complement data obtained on this receptor using protein chemical methods under denaturing conditions, where the existence of dimers was inferred (3). The model may also explain some other phenomena that have been observed for the D 2 dopamine receptor such as the observation of two rates of radioligand dissociation (31,45), the complex pH dependence of the binding of some ligands (46) (19,21), suggesting that higher order species than dimers may exist. The present data are, however, consistent with homodimers.…”

Section: Discussionmentioning

confidence: 72%

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Dopamine D2 Receptor Dimer Formation

Armstrong

Strange

2001

Journal of Biological Chemistry

113

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H]spiperone in the absence of sodium ions raclopride exerted noncompetitive effects, decreasing the number of sites labeled by the radioligand. These data are interpreted in terms of a model where the receptor exists as a dimer, and in the absence of sodium ions, raclopride exerts negative cooperativity across the dimer both for its own binding and the binding of spiperone. A model of the receptor has been produced that provides a good description of the experimental phenomena described here.The G-protein-coupled receptors (GPCRs) 1 constitute a large family of proteins responsible for the transduction of a wide range of signals (e.g. hormones, neurotransmitters, odorants, light, etc.) via G-proteins (1). GPCRs possess a common structural motif of seven ␣-helical membrane-spanning domains, and it is often assumed that the functional unit (i.e. the ligand binding and G-protein interaction domains) of the GPCR is wholly contained in a single polypeptide. Indeed, most models of GPCR function assume a monomeric receptor interacting with the G-protein (see, for example, Ref. 2). Several lines of evidence, however, suggest that the some GPCRs may exist in dimeric or oligomeric forms.Immunoblotting has in several cases revealed species corresponding not only to the predicted molecular weight of the receptor but also to multiples of the molecular weight. Bands corresponding to approximately twice the predicted molecular weight of the receptor have been interpreted as homodimers for several receptors including D 2 dopamine (3, 4), D 3 dopamine (5), ␤ 2 -adrenergic (6), substance P (7), opiate (8) and M 1 and M 2 muscarinic acetylcholine receptors (9). Co-immunoprecipitation has also been used to demonstrate homodimer formation for the ␤ 2 -adrenergic receptor (6), opiate receptor (8), and somatostatin SSTR5 receptor (10). In some cases, formation of heterodimers of GPCRs has been reported with differences in the pharmacological properties of the receptors in the heterodimer (e.g. GABA B receptor isoforms (11-13), ␦ and opiate receptors (14), dopamine, and somatostatin receptors (10)).Further evidence for interaction of GPCRs was provided by Maggio et al. (15), who created two chimeric receptors ␣ 2 /M 3 and M 3 /␣ 2 , in which the C-terminal regions (transmembrane domains VI and VII) were exchanged between the ␣ 2C adrenergic and M 3 muscarinic receptors. Expression of either chimera alone did not result in any detectable binding of typical radiolabeled muscarinic or adrenergic ligands. However, cotransfection of COS7 cells with both chimeras resulted in the appearance of binding activity corresponding to both native receptors. This has lead to the proposal that some GPCRs might form domain-swapped dimers (16). Evidence for GPCR interaction in cells has been obtained by expressing GPCRs fused to different chromophores. Transfer of energy between the chromophores has been shown for the ␤ 2 -adrenergic receptor (17) and somatostatin SSTR5 receptor (10) and provides good evidence for the close proximity of the two molecules...

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Section: Discussionsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 72%

Dopamine D2 Receptor Dimer Formation

Armstrong

Strange

2001

Journal of Biological Chemistry

113

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“…However, these electrodes are not stable with respect to cathodic polarization (11,12) since the complete protective layer of adsorbed oxygen is reduced, causing the local cell to be set up so that the reversible 02 potential is not recovered. Because passivation of Pt in HNO8 causes the Pt metal to be charged with dissolved oxygen to form a Pt-O alloy (8,11,12), the rest potential is higher (,-~I.IV) on the reduced Pt-O alloy/Of than on the Pt/O2 electrode. On such a reduced Pt-O alloy/O2 electrode a reproducible polarization curve can be obtained (11) exhibiting high values for the Tafel slope (0.266V) and for io (7.2 • 10-~ A-cmf).…”

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confidence: 99%

Some Aspects of the Reduction of Oxygen at a Platinum‐Oxygen Alloy Diaphragm

Hoare

1979

J. Electrochem. Soc.

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The steady-state galvanostatic polarization curve was obtained on the front side of a Pt aiaphragm in contact with O~-stirred 2N H2SO4 solution while the back side was in contact with concentrated HNOs. From low oxygen overvoltage (O2-~1) measurements it is shown that the rest potential is the reversible 02 l~otential. The rate of O2 reduction on the Pt-O alloy diaphragm is lower at high current densities than on a bright Pt cathode. At very high current densities the system is driven into the H2-evolution region where the H2-~ is close to the literature values for the Hf-TI on bright Pt. When the system was returned to open-circuit, the rest potential returned to the normal oxygen potential after about 24 hr. This time delay represents the time required to repair the complete layer of adsorbed oxygen atoms which had been removed by the strong cathodic current.

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“…1, curve A. When a sample of Pt is anodized, the surface becomes covered with a layer of adsorbed oxygen (Pt-O) 1 One of the reviewers requested that the DTA on pure gasfree Pt be made, but such a sample so far is not possible to obtain. To clean a Pt surface, it must be either heated in 02 or anodized which produces oxides on the surface and oxygen dissolved in the Pt metal (2,3).…”

Section: Discussionmentioning

confidence: 99%

On the Differential Thermal Analysis of the Platinum‐Oxygen System

Hoare

Paluch

Meibuhr

1976

J. Electrochem. Soc.

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Differential thermal analyses (DTA) curves were obtained on preanodized and HNOs-passivated platinum (Pt) samples. In both cases two kinds of adsorption states for oxygen on Pt were detected as well as oxygen dissolved in the interior of the Pt metal. The DTA results agree well with the cathodic stripping pulse data obtained earlier.From x-ray diffraction analysis and vacuum fusion studies on samples of bright Pt passivated in air-saturated concentrated HNO3, it was concluded (1) that the Pt metal contained enough dissolved oxygen to be considered a Pt-O alloy. It was also found that oxygen could be made to diffuse through a thin Pt foil (2) under conditions of strong anodic polarization (6 mA/ cm ~ at 2V) of the back side of the Pt diaphragm in solutions of H2804 and that this anodization process can cause relatively large quantities of oxygen to be dissolved in the Pt lattice (3,4). In these studies three kinds of sorbed oxygen were distinguished: surface adsorbed oxygen, dermasorbed oxygen dissolved in the first two or three metallic layers, and absorbed oxygen dissolved in the bulk of the metal. The properties of Pt-O alloys made by passivation in HNO3 were somewhat different from those made by anodization (3, 5, 6). The HNQ-passivated Pt is much more stable than the Pt-O alloy obtained from anodization (6).Babenkova et al. (7) investigated the forms of hydrogen sorbed by palladium by measuring the desorption of hydrogen during a linearly programmed temperature rise experiment. They were able to find two forms of adsorbed hydrogen on the surface as well as the hydrogen dissolved in the bulk Pd.It seemed likely that a differential thermal analysis (DTA) of the platinum-oxygen system might enable one to observe the various forms of oxygen sorbed by Pt as well as to shed light on possible differences in the structure of Pt-O alloy formed by HNO3 passivation or by anodization.This report describes some DTA experiments made on Pt-O alloys. ExperimentalAll DTA curves were obtained with a furnace platform assembly with which analyses may be made on the sample in any controlled atmosphere at pressures ranging from 1.3 • 10 -6 to 2 atm. The reference sample was A1203 which is thermally inert in the temperature range of the scan, 0-1000~ The Pt-O alloy samples were made from small beads (0.11 cm in diameter) melted at the end of a Pt(99.99% pure) wire. These beads were cleaned by repeatedly heating to white heat in a H2 jet followed by quenching in concentrated HNO3. Afterward, three beads were mounted in a Teflon cell filled with concentrated HNO~ (70%) to soak for periods of time greater than 72 hr (6). Another set of three Pt beads were mounted in a Teflon cell filled with 2N H2SO4 solution and were anodized at 6 mA/cm 2 (2.00 • 0.05V) against a Pt gauze counterelectrode for periods of time greater than 24 hr. All Pt-O alloy samples were made at room temperature (24 ~ • 1~After formation of the Pt-O alloy, a bead was cut off of the wire and weighed ,-~37 mg) in a small Pt dish of * Electrochemical Society Active Mem...

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Closure to “Discussion of ‘On the Differential Thermal Analysis of the Platinum‐Oxygen System’ [J. P. Hoare, R. F. Paluch, and S. G. Meibuhr (pp. 1821–1824, Vol. 123, No. 12)]”

Cited by 6 publications

References 0 publications

Dopamine D2 Receptor Dimer Formation

Dopamine D2 Receptor Dimer Formation

Some Aspects of the Reduction of Oxygen at a Platinum‐Oxygen Alloy Diaphragm

On the Differential Thermal Analysis of the Platinum‐Oxygen System

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