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At least 253 records · Page 14Linked to original sources

PubMed1996

G-protein-coupled receptor regulation: role of G-protein-coupled receptor kinases and arrestins.

G-protein-coupled receptors (GPCRs) represent a large family of proteins that transduce extracellular signals to the interior of cells. Signalling through these receptors rapidly desensitized primarily as the consequence of receptor phosphorylation, but receptor sequestration and downregulation can also contribute to this process. Two families of serine/threonine kinases, second messenger dependent protein kinases and receptor-specific G-protein-coupled receptor kinases (GRKs), phosphorylate GPCRs and thereby contribute to receptor desensitization. Receptor-specific phosphorylation of GPCRs promotes the binding of cytosolic proteins referred to as arrestins, which function to further uncouple GPCRs from their heterotrimeric G-proteins. To date, the GRK protein family consists of six members, which can be further classified into subgroups according to sequence homology and functional similarities. The arrestin protein family also comprises six members, which are subgrouped on the basis of sequence homology and tissue distribution. While the molecular mechanisms contributing to GPCR desensitization are fairly well characterized, little is known about the mechanism(s) by which GPCR responsiveness is reestablished, other than that receptor sequestration (internalization) might be involved. The goal of the present review is to overview current understanding of the regulation of GPCR responsiveness. In particular, we will review new evidence suggesting a pleiotropic role for GRKs and arrestins in the regulation of GPCR responsiveness. GRK-mediated phosphorylation and arrestin binding are not only involved in the functional uncoupling of GPCRs but they are also intimately involved in promoting GPCR sequestration and as such likely play an important role in mediating the subsequent resensitization of GPCRs.

Animals↗

PubMed2000

Microsphere resonators strongly coupled to a plane dielectric substrate: coupling via the optical near field.

A model is proposed that describes the essential optical process in the recently observed resonant light scattering from a microsphere resonator that is strongly coupled to the substrate. The experimentally observed field patterns across the resonance can be reproduced quite well by a numerical calculation taking into account only a few vector spherical waves that are converted from nonpropagating to propagating waves at the substrate surface. Explicit consideration of the multiple-reflection effect is not necessary to reproduce the experimental results. Comparison of the experiment and the calculation suggests the splitting of degenerate resonance modes that have different azimuthal mode numbers within a single broad resonance line. These results are discussed on the basis of the strongly coupled nature of the system.

Electricity↗

PubMed2004

External-cavity, actively mode-locked grating-coupled surface-emitting laser and amplification characteristics of a grating-coupled semiconductor optical amplifier.

An external-cavity, actively mode-locked grating-coupled surface-emitting semiconductor laser (GCSEL) is demonstrated for the first time to the authors' knowledge. The mode-locked oscillator generates a train of optical pulses at a 297-MHz pulse-repetition frequency. The optical pulse from the oscillator has a width of 22.6 ps and a spectral bandwidth of 0.07 nm at 975.9 nm, giving a time-bandwidth product of 0.50. In addition, amplification characteristics of a grating-coupled semiconductor optical amplifier are studied with a continuous-wave external-cavity GCSEL.

Journal Article↗

PubMed2005

Preconcentration and determination of trace metals in seawater using a thiol cotton fiber minicolumn coupled with inductively coupled plasma mass spectrometry.

A rapid separation and preconcentration method was developed for the determination of trace metals Cu, Zn, Cd, and Pb in seawater using a minicolumn packed with thiol cotton fiber (TCF) coupled with inductively coupled plasma mass spectrometry (ICP-MS). Preconcentration parameters, such as seawater sample volume and flow rate and eluent hydrochloric acid concentration, volume and flow rate, were optimized. Under the optimized conditions, trace metals Cu, Zn, Cd, and Pb in seawater can be determined with no interference from saline matrices. When a sample volume of 1500 ml and a sample flow rate of 15 ml min(-1) were used, the preconcentration factor of 1500 and RSD value of <7% at ng ml(-1) were achieved. The accuracy of the recommended method was verified by the analysis of certified reference materials.

Journal Article↗

PubMed2006

Functionalized ionic liquids as new supports for peptide coupling and traceless catalyzed carbon-carbon coupling reactions.

A new strategy to obtain pure ionic liquid support with a high loading (3 mmol/g) of primary amino groups is reported. The compatibility of the imidazolium unit was demonstrated with DIC or DCC coupling reactions of protected amino acids and with classical cleavage of BOC or Fmoc protecting groups. In addition, this is the first report of a traceless ionic liquid support based on a silicon linker with a high loading (3 mmol/g) of aryl bromide reactive groups used in a palladium-catalyzed carbon-carbon coupling reaction.

Carbon↗

PubMed1981

Comparison of acoustically coupled and mechanically coupled speech.

Phonetically balanced work lists were mechanically coupled onto the ossicular chain of anesthetized guinea pigs by piezoelectric-type drivers and the resulting cochlear microphonic (CM) recorded on magnetic tape. Similar recordings of the CM resulting from free field tympanic membrane stimulation by hi-fi speakers were also obtained. The recordings were compared by conventional discrimination testing. In discrimination testing of all the raw recordings, listeners achieved essentially perfect scores. Addition of masking noise sufficient to reduce mean discrimination scores to 65-70% revealed no significant discrimination differences. When piezoelectrically initiated, CM-derived lists were compared with similar lists passed through hearing aids in an anechoic chamber, the preference of a panel of listeners for the quality of mechanically coupled speech was significantly higher. Mechanical-acoustical displacement equivalency at normal physiological levels and freedom from mechanical-electrical artifact were demonstrated by measurement of ossicular chain displacement by a fiber optic lever displacement transducer.

Animals↗

PubMed1990

Simultaneous multielement analysis of diet samples by inductively coupled plasma mass spectrometry and inductively coupled plasma atomic emission spectrometry.

Diet samples were collected by a duplicated portion study for an adult male in both Mito, Japan and Los Alamos, U.S.A. The ashed samples were analyzed with inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled atomic emission spectrometry (ICP-AES) for 22 elements. The trace and ultratrace elements, Ba, Mo, Ni, Co, Cd, Cs, Tl, Pb, Bi, Th, and U were determined by ICP-MS. The major and minor elements, Na, K, P, Ca, Mg, Fe, Zn, Mn, Al, Sr, and Cu were determined by ICP-AES. Accuracy and precision for some elements were examined by analyzing National Institute of Standards and Technology (formerly National Bureau of Standards) Standard Reference Materials, 1577b Bovine Liver, and 1573 Tomato Leaves. Simultaneous multielement analyses of diet samples by using the two methods were found to be very useful.

Adult↗

PubMed2004

Analysis of phosphorus herbicides by ion-pairing reversed-phase liquid chromatography coupled to inductively coupled plasma mass spectrometry with octapole reaction cell.

A reversed phase ion-pairing high performance liquid chromatographic (RPIP-HPLC) method is developed for the separation of two phosphorus herbicides, Glufosinate and Glyphosate as well as Aminomethylphosphonic acid (AMPA), the major metabolite of Glyphosate. Tetrabutylammonium hydroxide is used as the ion-pairing reagent in conjunction with an ammonium acetate/acetic acid buffering system at pH 4.7. An inductively coupled plasma mass spectrometer (ICP-MS) is coupled to the chromatographic system to detect the herbicides at m/z = 31P. Historically, phosphorus has been recognized as one of the elements difficult to analyze in argon plasma. This is due to its relatively high ionization potential (10.5 eV) as well as the inherent presence of the polyatomic interferences 14N16O1H+ and 15N16O+ overlapping its only isotope at m/z = 31. An octapole reaction cell is utilized to minimize the isobaric polyatomic interferences and to obtain the highest signal-to-background ratio. Detection limits were found to be in the low ppt range (25-32 ng/l). The developed method is successfully applied to the analysis of water samples collected from the Ohio River and spiked with a standard compounds at a level of 20 microg/l.

Aminobutyrates↗

PubMed2004

Liquid chromatography coupled with inductively coupled plasma mass spectrometry in the pharmaceutical industry: selected examples.

Both LC and capillary LC (CapLC) have been successfully interfaced with inductively coupled plasma mass spectrometry (ICP-MS). Gradients of acetonitrile and aqueous based solvents have been employed to separate several compounds of pharmaceutical interest. This paper will describe four application areas in the pharmaceutical industry, and examples will be shown where CapLC, LC and gel electrophoresis via laser ablation have been coupled with ICP-MS. The four areas highlighted in this paper are: (1) the use of derivatisation reactions to "make the invisible visible". Methods involving derivatisations with copper and iron will be described that can be used for the analysis of amines and carboxylic acids by ICP-MS. (2) The profiling of metal ion content (in particular bromine) in biological samples such as human plasma, this study will focus on the metabolism of bromine-labelled peptides (e.g. substance P). (3) The analysis of materials derived from single, solid-phase beads used in combinatorial chemistry, and (4) also discussed will be our findings from investigations into the use of laser ablation ICP-MS on the determination of protein phosphorylation on electrophoresis gel blots.

Chromatography, Liquid↗

PubMed1992

Stimulation by thyroid hormone of coupled respiration and of respiration apparently not coupled to the synthesis of ATP in rat hepatocytes.

Maximal rates of O2 uptake by hepatocytes from hypothyroid, euthyroid, and hyperthyroid rats, in the absence of uncoupling agents or ionophores, were achieved by simultaneously stimulating ureogenesis and gluconeogenesis. Rates were increased by pretreatment of the donor animals with thyroid hormone. Only a minor part of the increase could be attributed to stimulation of the activity of plasma membrane (Na+ + K+)-ATPase. No synthesis of glycogen occurred, nor was there any evidence of pyruvate cycling under the conditions used, thus ruling out these processes as potential sources of ATP turnover. Calculation of the O2 uptake necessary to satisfy the energy requirements of gluconeogenesis and ureogenesis, based on anticipated ATP demand and an assumed P:O ratio of 3:1, invariably yielded a theoretical quantity that was less than the experimentally measured increase in O2 uptake. The difference between measured and calculated rates of respiration, possibly representing noncoupled respiration, was related to the thyroid status of the animal, being greatest in cells from hyperthyroid rats. In another experimental approach the O2 uptake associated with ATP synthesis was inhibited by the addition of oligomycin to hepatocytes incubated in the presence of substrates, thus abolishing ATP-coupled respiration. The magnitude of the ATP-coupled as well as the residual respiration was increased in response to thyroid hormone. Thyroid hormone increased the turnover of intramitochondrial ATP. These results imply that a considerable portion of the thermogenic effect of thyroid hormone may be mediated by a stimulatory action on metabolism not directly associated with extramitochondrial ATP-dependent synthetic processes.

Adenosine Triphosphate↗

PubMed2004

[Characterization of Hg-binding metallothioneins in tissues of rat after oral intake of mercury chloride by size-exclusion chromatography coupled with inductively coupled plasma-mass spectrometry].

Hg concentrations, total metallothioneins (MTs) and metal-binding MTs in tissues of the rat after oral intake of HgCl2 were determined by the inductively coupled plasma-mass spectrometry (ICP-MS), a modifield mecurry saturarion assay and the size-exclusion chormatography (SEC) coupled with ICP-MS, respectively. The results indicated that Hg accumulation in all of the rat tissues, including kidney, liver, testicle, brain, heart, serum and blood plasma, in HgCl2 group significantly increased compared with that in the control group, especiallyin kidney,liver and testicle. A large amount of MTs was inducted in these exposed rat tissues, especially in their kidneys and livers. The metal species binding with MTs obtained with SECICP-MS showed that the fractions of Hg-MTs in both kidney and liver of exposed rat were significantly higher compared with those of the control. In addition, higher amounts of Cu-MTs observed in exposed rat liver and kidney demomstrated the effect of MTs in the homeostatis of Cu and in the detoxification of Hg.

Animals↗

PubMed1984

Studies in the enhancement of tumour immunity by coupling strong antigens to tumour cells ('heterogenization of tumours'). Helper T cell clones against PPD help other T cells mount anti-tumour responses to PPD-coupled tumour cells.

PPD-reactive T cell clones have been used to analyse the nature of T lymphocytes that are involved in the 'heterogenization' of tumour cells. This is a phenomenon where coupling tumour cells to a strong antigen (in this case PPD) causes an enhanced immune response to tumour-specific antigens to be elicited providing that the host shows T cell immunity to the strong antigen (in this case is BCG positive). Clones of T cells with the Lyt1+2- phenotype which were unable to mediate delayed-type hypersensitivity but which provided efficient help to hapten-primed B cells were found to potentiate anti-tumour immunity in BCG-negative syngeneic mice when immunized with Con-A-PPD coupled, X-irradiated MC6A tumour cells. There therefore appears to be a mechanism whereby a helper T cell response to one antigen can provide help for the generation of a T cell response to a linked antigen which is analogous to the well-known phenomenon of help to hapten primed B cells. Furthermore the clones of T cells that help B cells the best are those that give maximal augmentation of T cell immunity.

Animals↗

PubMed1994

Mutation of an aspartate residue highly conserved among G-protein-coupled receptors results in nonreciprocal disruption of alpha 2-adrenergic receptor-G-protein interactions. A negative charge at amino acid residue 79 forecasts alpha 2A-adrenergic receptor sensitivity to allosteric modulation by monovalent cations and fully effective receptor/G-protein coupling.

We have mutated the aspartate residue in the putative second transmembrane spanning domain of the alpha 2A-adrenergic receptor (alpha 2AAR) to the non-negatively charged asparagine (D79N) and glutamine (D79Q) and the negatively charged glutamate (D79E) residue in an effort to better characterize the role of this residue, highly conserved among G-protein-coupled receptors, in Na+ regulation of ligand binding and in receptor G-protein coupling. Allosteric modulation of receptor-ligand interactions by Na+ is retained by the D79E alpha 2AAR but lost upon mutation to the uncharged D79N and D79Q residues. Loss of allosteric effects of Na+ is paralleled by a complete loss of retrograde information transfer from G-proteins to alpha 2AAR in AtT20 cells, measured via the sensitivity of radiolabeled agonist binding to Gpp(NH)p. In contrast to the complete elimination of retrograde signaling via the D79N and D79Q alpha 2AAR, anterograde information transfer from receptor to G-protein is modified in a more subtle quantitative way, since agonist-stimulated GTPase activity via D79N and D79Q alpha 2AAR, although apparently attenuated compared to wild type and D79E alpha 2AAR, is no less than the GTPase activity elicited by endogenous somatostatin receptors in AtT20 cells. These data indicate that a negative charge at amino acid residue 79 forecasts sensitivity to allosteric regulation by monovalent cations and its mutation to non-negatively charged residues elicits a nonparallel modulation of receptor-->G-protein versus G-protein-->receptor communication between alpha 2AAR and pertussis toxin-sensitive GTP-binding proteins.

Allosteric Regulation↗

PubMedDate not supplied

Evaluation of the importance of Chlamydia T. and/or Mycoplasma H. and/or Ureaplasma U. genital infections and of antisperm antibodies in couples affected by muco-semen incompatibility and in couples with unexplained infertility.

Both the male and female partners of 28 couples with muco-semen incompatibility and of 8 couples with unexplained infertility were examined for the presence of genital infections by Chlamydia T. and/or Mycoplasma H. and/or Ureaplasma U. (CMU infections), and for topical and serum antisperm antibodies (AS-abs). The presence of other common genital infections, and for Candida A. and Trichomonas had previously been excluded in all the subjects; all the female partners presented normal hysterosalpingographs, regular ovulatory function and cervical score > or = 10. The main cause of the muco-semen incompatibility was dysspermia (35.7%), either associated or not with male CMU infections, followed by female CMU infections (21.4%), male CMU infections without dysspermia (3.6%), and the presence of AS-abs in the mucus (3.6%) and in the semen (3.6%); in 32.6% of the cases no plausible explanation was found for muco-semen incompatibility. In 42.8% CMU infections were implicated in the muco-semen incompatibility; furthermore, there was associated dysspermia in 50% of the cases. AS-abs were found in the mucus or in the serum of 70% of the patients with CMU infections, while this figure went down to 34.6% in subjects not affected by such infections. None of the patients with CMU infections showed AS-abs either in the semen and/or in the serum. AS-abs were found in the serum of 25% of the female patients with so-called "unexplained" infertility. CMU infections are important for the determination of muco-semen incompatibility, both with and without dyspermia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1997

Gamete donation from couple to couple in the new French law.

In practice, the partners or spouses of gamete donors are frequently asked permission for the donation. The new French law on bioethics of 29 July 1994 requires that: a) the donor should be one of a couple that has already procreated and b) the written consent of the partner or spouse is obtained. These conditions lead not only to several practical problems in the organisation of donor insemination but also reject a large part of the potential donor population. The two basic qualities demanded of the donors, e.g., paternity and stable relationship, are analyzed. It is proposed that only fatherhood should serve as an exclusionary criterion for sperm donation. The donor need not be a part of a couple at the moment of the donation but if he has a partner at that time her opinion should be heard.

Cross-Cultural Comparison↗

PubMed1998

Trimeric G alpha beta gamma protein coupling to a 3D model of G protein-coupled receptors confirming a new molecular mechanism for activation.

The present-day model for G protein activation and the associated theory on how a G protein-coupled receptor may activate the G protein are summarized. Experimental data are outlined which seem not to be in accordance with this present-day model. An alternative molecular mechanism for ternary complex activation is presented together with a three-dimensional model for a receptor coupled to the appropriate trimeric G protein. This 3D structure confirms our new molecular mechanism of activation.

GTP-Binding Proteins↗

PubMed1975

The action of tributyltin on energy coupling in coupling-factor-deficient submitochondrial particles.

1. Tributyltin at concentrations of approx. 1nmol/mg of protein induces respiratory control and lessens the protein permeability of coupling-factor-deficient submitochondrial particles. 2. At these concentrations or lower, it increases the P/O ratio of the particles to a small extent and inhibits the adenosine triphosphatase activity without greatly increasing its sensitivity to uncoupling agents. 3. It fails to stimulate ATP-driven reversed electron transport or transhydrogenase, but stimulates the transhydrogenase driven by aerobic succinate oxidation. 4. The results indicate that, unlike oligomycin, tributyltin does not discriminate between damaged and intact ATP-synthesizing complexes. 5. The relationship between the oligomycin- and tributyltin-binding sites is discussed.

Adenosine Triphosphatases↗

PubMed2000

Direct genetic demonstration of G alpha 13 coupling to the orphan G protein-coupled receptor G2A leading to RhoA-dependent actin rearrangement.

G2A is an orphan G protein-coupled receptor (GPCR), expressed predominantly in T and B cells and homologous to a small group of GPCRs of unknown function expressed in lymphoid tissues. G2A is transcriptionally induced in response to diverse stimuli, and its ectopic expression suppresses transformation of B lymphoid precursors by BCR-ABL. G2A induces morphological transformation of NIH 3T3 fibroblasts. Microinjection of constructs encoding G2A into Swiss 3T3 fibroblasts induces actin reorganization into stress fibers that depends on RhoA, but not CDC42 or RAC. G2A elicits RhoA-dependent transcriptional activation of serum response factor. Direct evaluation of RhoA activity demonstrates elevated levels of RhoA-GTP in G2A-expressing cells. Microinjection of embryonic fibroblasts derived from various G alpha knockout mice establishes a requirement for G alpha 13 but not G alpha 12 or G alpha q/11 in G2A-induced actin rearrangement. In conclusion, G2A represents a family of GPCRs expressed in lymphocytes that may link diverse stimuli to cytoskeletal reorganization and transcriptional activation through a pathway involving G alpha 13 and RhoA.

Actins↗