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J C Meunier

Publications and source records attributed to J C Meunier.

At least 109 records · Page 6Linked to original sources
PubMed1986

Structural, immunological and kinetic comparisons of NADP-dependent malate dehydrogenases from spinach (C3) and corn (C4) chloroplasts.

This paper compares structural, immunological and kinetic properties of corn (C4) and spinach (C3) NADP-malate dehydrogenases. These chloroplastic enzymes are regulated in vivo by thiol-disulfide interchange. Both in their oxidized (inactive) and reduced (active) states these enzymes have a dimeric structure with molecular masses for the subunit ranging from 28 kDa to 38 kDa according to the procedure used for the determination. These enzymes are thus structurally related. The use of specific antibodies showed that they are also immunologically related although not identical. Finally both enzymes showed close kinetic properties with comparable kcat and Km. Since C4 plants have approximately ten times more NADP-malate dehydrogenase activity than C3 plants, these data suggest that the differences in activities are probably related to the enzyme content of each plant type.

Antigen-Antibody Reactions↗
PubMed1986

Synthesis and biological activities of dynorphin A analogues with opioid antagonist properties.

Dynorphin A, which displays a wide variety of physiological effects, binds to opioid receptors preferentially at the kappa receptor type. kappa-selective antagonists would be very useful as pharmacological and biochemical probes to study and better understand the action of dynorphin A at its preferred receptor. However, the development of such molecules has been elusive, and very few are known at this time. Taking these features into account, we have synthesized by the solid-phase procedure several analogues of dynorphin A containing various D-amino acid substitutions. The binding properties of the peptides have been examined at three main opioid binding sites (mu, delta, and kappa) and their kappa selectivity determined. Their biological activities have been tested in three specific pharmacological assays for agonist and/or antagonist properties. Introduction of D-Trp substitution leads to analogues, in particular [D- Trp2,8,D-Pro10]-, [D-Trp5,8,D-Pro10]-, and [D-Trp2,4,8,D-Pro10]dynorphin(1-11), showing antagonist properties in the isolated rabbit vas deferens preparation, a kappa specific bioassay. The antagonism against dynorphin A is weak, as indicated by the observed Ke values (433, 199, and 293 nM, respectively), and not very selective (kappa vs. mu). Such peptide analogues derived from the endogenous ligand and endowed with antagonist properties are the first ones reported to date and could open a promising way in designing more potent and selective kappa opioid antagonists.

Animals↗
PubMed1986

Differential regulation of two molecular forms of a mu-opioid receptor type by sodium ions, manganese ions and by guanyl-5'-yl imidodiphosphate.

The rabbit cerebellum contains a very high proportion (up to 80%) of mu-opioid receptor sites (Meunier, J.C., Kouakou, Y., Puget, A. and Moisand, C., Mol. Pharmacol. 24, 23-29, 1983). A membrane fraction derived therefrom is labeled either with the opioid agonist, 3H-etorphine or with the opioid antagonist, 3H-diprenorphine, and solubilized with digitonin. Centrifugation of the soluble extracts in linear sucrose gradients reveals that bound 3H-etorphine sediments faster than does bound 3H-diprenorphine: 12S vs 10S. Pre-incubation of membranes and radioligand in the presence of 120 mM NaCl results in considerably decreased recovery of the 3H-agonist in 12S form while recovery of the 3H-antagonist in 10S form is substantially increased. The opposite situation is observed when the membranes have been prelabeled with radioligand in the presence of 1 mM MnCl2. Guanyl-5'-yl imidodiphosphate, a metabolically stable structural analog of GTP is found to selectively reduce recovery of labeled 12S receptors while it does not affect that of labeled 10S receptors. These data indicate that the mu-opioid receptor from rabbit cerebellum is capable of existing in two forms which differ in apparent molecular size: an "antagonist" (10S) form of apparent Mr approximately 230,000 which is stabilized in the presence of sodium ions and an "agonist" (12S) form of apparent Mr approximately 300,000 which, unlike the antagonist one, is sensitive to guanyl-5'-yl imidodiphosphate. It is thought that the form of larger apparent size represents the mu-opioid receptor associated with a guanine nucleotide regulatory protein.

Adenylyl Cyclases↗
PubMed1986

Characterization, solubilization and purification of an opioid receptor from the brain of the frog Rana ridibunda.

The brain of the frog R. ridibunda contains a major opioid binding site which in vitro pharmacological profile is different from those of mammalian mu, delta- and kappa-opioid sites. In digitonin extracts, this major opioid site exists as two molecular forms -10S and 12S- which are clearly resolved by sedimentation in sucrose gradients and which are thought to represent the opioid receptor alone (10S) or associated (12S) with a guanine nucleotide regulatory protein. Purification of the digitonin extracts by affinity chromatography on immobilized dynorphin, results in a single major protein component of apparent Mr approximately 64,000.

Animals↗
PubMed1986

125I-DPDYN, monoiodo [D-Pro10]- dynorphin (1-11), is an effective and useful tool for the study of kappa opioid receptors.

Iodination of the kappa-selective peptide DPDYN, [D-Pro10]-dynorphin (1-11), has been performed. The non radioactive monoiodo derivative of DPDYN retains kappa-selectivity (kappa/mu = 48 and kappa/delta = 140), despite a general but moderate decrease in affinity. Radioiodination of DPDYN leads to the monoiodinated peptide (S.A 700-800 Ci/mmol) which interacts specifically and reversibly with the kappa-sites in guinea-pig cerebellum membranes with high affinity (KD = 0.12-0.18 nM). In guinea-pig brain (mu-delta-kappa) and rabbit cerebellum (kappa much less than mu), 125I-DPDYN discriminates between kappa- and other (mu, delta) binding sites. We have used this new labelled probe for the direct, precise and rapid (exposure time less than 100 hours) visualization of kappa-sites in guinea-pig and rabbit cerebellar slices using autoradiography.

Animals↗
PubMed1985

Na+ ions and Gpp(NH)p selectively inhibit agonist interactions at mu- and kappa-opioid receptor sites in rabbit and guinea-pig cerebellum membranes.

Rabbit and guinea-pig cerebellum membrane preparations contain a high proportion (greater than 80%) of mu- and of kappa-opioid binding sites, respectively. These preparations were therefore used to compare the regulation of binding of mu- and of kappa-opioid agonists and antagonists by sodium ions and by guanyl-5'-yl imidodiphosphate. We report here that Na+ ions, Gpp(NH)p and most efficiently, the two agents in association selectively inhibited binding of opioid agonists not only in the mu preparation (rabbit cerebellum) but also in the kappa preparation (guinea-pig cerebellum). These allosteric effectors did not inhibit equilibrium binding of antagonists (naloxone, Mr 2266 or diprenorphine) in the two preparations. Taken together these results suggest that occupancy either of the mu-receptor by a mu-agonist or of the kappa-receptor by a kappa-agonist may be accompanied by similar if not identical molecular events. They also suggest a method to rapidly screen newly designed drugs as mu- or kappa-opioid agonists or antagonists.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1984

The 'slow' pH-induced conformational transition of chloroplast fructose 1,6-bisphosphatase and the control of the Calvin cycle.

A slow conformation change of chloroplastic reduced fructose bisphosphatase is detected upon raising the pH from 7 to 8 or upon lowering the pH from 8 to 7. These conformation changes are fully reversible. In the time scale investigated these processes occur in one step. Their time constants and their amplitudes have been determined and analyzed as a function of proton concentration. The results obtained are consistent with the view that upon ionization or protonation of a strategic ionizable group the protein undergoes a 'slow' conformational transition that may be followed by conventional fluorescence techniques. Since illumination brings about a pH rise of chloroplastic stroma from 7 to 8, the above results suggest that light activation of fructose bisphosphatase is at least in part due to a slow conformation change of this enzyme.

Chloroplasts↗
PubMed1984

Affinity chromatography, on fructose-bisphosphatase-Sepharose, of two chloroplastic thioredoxins F. Purification and comparative molecular properties.

A new method of purification of chloroplastic thioredoxins has been presented. This method is based on affinity chromatography on fructose-bisphosphatase--Sepharose columns. Two thioredoxin, fA and fB, may be extracted and purified to homogeneity from the same leaf extract. Whereas fA is monomeric and has an Mr of 11 400 +/- 500, fB is dimeric with an Mr of 18 000 +/- 600. The dimer dissociates in two halves in the ultracentrifuge under the effect of high pressures. Raising the ionic strength results in the same effect. Thioredoxins fA and fB activate to similar extents chloroplastic fructose bisphosphatase and NADP--malate dehydrogenase. Chloroplastic sedoheptulose bisphosphatase is activated by thioredoxin fB but not by thioredoxin fA.

Centrifugation, Density Gradient↗
PubMed1984

Divalent cations: do they stabilize the agonist (12S) form of the mu opioid receptor?

In rabbit cerebellum membranes, millimolar concentrations of Mn++ ions while slightly reducing the Kd of 3H-etorphine counteract, to a large extent, sodium inhibition of equilibrium binding of the tritiated agonist to the mu opioid receptor. In digitonin extracts of membranes which have been incubated either with 3H-etorphine or with 3H-diprenorphine in the presence of Mn++ ions, recovery of radioligand bound to the agonist form of the receptor (sedimenting at position 12S) is substantially increased while, at the same time, recovery of radioligand bound to the antagonist form of the receptor (10S) is markedly reduced. Taken together these results suggest that Mn++ ions stabilize the agonist (12S) form of the mu opioid receptor. Mn++ ions may do so by promoting association of the receptor and of a guanine nucleotide regulatory protein.

Animals↗
PubMed1984

Solubilization of two molecular forms of the frog brain opioid receptor.

In equilibrium binding studies, using 3H-etorphine and 3H-diprenorphine, digitonin extracts of frog brain membranes are found to contain two classes of sites, one of which is seen only in the presence of Na+ ions. Centrifugation of the extracts in sucrose gradients separates two macromolecular components (10S and 12S) which display specific opiate binding activity. The 12S component appears to carry the site that binds opiates in the absence of Na+ ions while the 10S component would carry the other site, i.e. the one which is seen only in the presence of Na+ ions in equilibrium binding studies. Preliminary evidence is also given that in extracts of frog brain membranes which have been pre-incubated with 120 mM NaCl, the balance of the two components is shifted in favor of the slower sedimenting (10S) one. These results are discussed in terms of the regulation of the state of equilibrium between an agonist (12S) and an antagonist (10S) form of the opioid receptor.

Animals↗
PubMed1984

[Basal concentrations and postprandial integrated flows of gastrin in patients with atrophic gastritis or duodenal ulcer. Limits of diagnostic usefulness].

Maximal acid outputs were determined during intravenous pentagastrin tests (6 micrograms/kg/h) in 119 male subjects: 17 controls, 74 patients with duodenal ulcer and 28 with atrophic gastritis. Basal and postprandial serum gastrin levels were also determined in order to estimate the integrated gastrin response to the meal. In patients with atrophic gastritis the maximal acid output was decreased (p less than 0.01) and the integrated gastric response was increased (p less than 0.01) but the basal gastrin levels in these patients did not differ from that of controls. An integrated gastrin response greater than 2.5 ng/ml/100 min was observed in 89 p. 100 of patients with atrophic gastritis. An integrated gastrin response smaller than 2.5 ng/ml/100 min was observed in 76 p. 100 of controls. The maximal acid output was smaller than 20 mmol/l in all patients with atrophic gastritis but was greater than this value in all controls. In duodenal ulcer patients, the measured parameters were not significantly different from control values. The measure of the integrated gastrin response which reflects the presence of an antral endocrine hyperactivity may be useful to detect patients with atrophic gastritis, but this test is less sensitive and less specific than the determination of the maximal acid output.

Duodenal Ulcer↗
PubMed1983

Physical separation of the agonist and antagonist forms of a mu opiate receptor?

The rabbit cerebellum contains up to 80% of mu opiate binding sites (J.C. Meunier, Life Sci. 31, 1327-1330 (1982) ). A crude membrane fraction derived therefrom was labelled either with the opiate agonist: 3H-etorphine or with the opiate antagonist: 3H-diprenorphine, and solubilized with digitonin. Centrifugation of the soluble extracts in linear sucrose gradients reveals that bound 3H-etorphine sediments faster than does bound 3H-diprenorphine: 12S vs 10S. The 3H-etorphine macromolecular complex (12S) is virtually absent in extracts of membranes that have been labelled in the presence of 120 mM NaCl or of 50 microM Gpp(NH)p (guanyl-5'-yl imidodiphosphate). Under the same conditions, recovery of 3H-diprenorphine in bound (10S) form is either not affected (Gpp(NH)p) or substantially increased (NaCl). These data are consistent with the notion that cerebellar mu opiate receptors may exist under physically separable agonist and antagonist states.

Animals↗
PubMed1983

Distinct molecular forms of opiate binding in the frog brain.

In frog brain membranes, equilibrium saturation binding of the opiate agonist: 3H-etorphine and of the opiate antagonist: 3H-diprenorphine is biphasic. In the presence of sodium ions (120 mM), "kinetic conversions" (unchanged Bmax) are observed: high affinity binding of the 3H-agonist is decreased while high affinity binding of the antagonist is increased. Frog brain membranes were labelled either with 3H-etorphine or with 3H-diprenorphine and solubilized with digitonin. The soluble extracts were centrifuged in sucrose gradients: two distinct components were labelled which sedimented respectively faster (approximately 12 S) and slower (approximately 10 S) than did catalase, used as marker. Pre-incubation of membrane and of 3H-ligand in the presence of 120 mM NaCl resulted in 1) considerably reduced recovery of the 12 S component in labelled form and 2) substantially enhanced labelling of the 10 S component with the 3H-antagonist. Gpp(NH)p (guanyl-5'-yl imidodiphosphate) exerted similar effects as did sodium ions. Taken together, these data suggest that the two components in question represent physically distinct agonist and antagonist forms of frog brain opiate receptors.

Animals↗
PubMed1983

Multiple opiate binding sites in the central nervous system of the rabbit. Large predominance of a mu subtype in the cerebellum and characterization of a kappa subtype in the thalamus.

We have compared the binding characteristics of [3H]etorphine, a nonselective mu-, delta-, and kappa-opiate agonist, with those of [3H]Tyr-D-Ala-Gly-MePhe-NH(CH2)2OH ([3H]DAGO), a selective mu-agonist, in rabbit cerebellar and thalamic membranes. We have also examined the ability of various unlabeled opioid ligands to compete with the binding of [3H]etorphine in the two preparations. In cerebellar membranes, [3H]DAGO(Kd = 0.7 nM) labels slightly fewer sites than does [3H]etorphine (Kd = 0.06 nM): 0.18 versus 0.24 pmole/mg of protein. In addition, competition studies indicate that up to 75% of the [3H]etorphine binding sites in this preparation display (a) high apparent affinity for unlabeled DAGO and (b) higher apparent affinity for morphine, the prototypical mu-agonist, than for Tyr-D-Ala-Gly-Phe-D-Leu (DADL), a delta-agonist. Together, these results suggest that the rabbit cerebellum contains a very high proportion (0.7-0.8) of mu-opiate binding sites. In thalamic membranes, [3H]DAGO (Kd = 1.1 nM) labels considerably fewer sites than does [3H]etorphine (Kd = 0.08 nM): 0.09 versus 0.27 pmole/mg of protein. In this preparation, the competition curves of DAGO and of DADL resolve binding of [3H]etorphine into two components. The first component accounts for 40-50% of total binding and reflects the interaction of [3H]etorphine with mu-opiate binding sites. The second component (up to 50% of total binding) is unaffected in the presence of DADL at concentrations (1-10 microM) that rule out binding of [3H]etorphine to mu- and delta-opiate binding sites. It disappears readily in the presence of very low concentrations (Ki less than 1 nM) of benzomorphan opiates (bremazocine, cyclazocine, and ethylketocyclazocine) yet it is relatively insensitive to inhibition by mu- and delta-agonists. This second component may therefore reflect [3H]etorphine's interaction with a kappa-opiate binding site. The kappa-opiate binding site is assayed for as that site which binds [3H]etorphine (0.5 nM) in the presence of either DADL (2 microM) or 10 microM of another enkephalin: Tyr-D-Ser-Gly-Phe-Leu-Thr. We find that, in the rabbit central nervous system, the thalamus, followed by frontal cortex and caudate nucleus, shows the highest content of kappa-opiate binding sites.

Animals↗
PubMed1983

[Opiate receptor(s) of the frog brain: soluble-phase separation of the macromolecular complexes of an agonist and an antagonist].

Frog brain membranes, pre-labelled with the opiate agonist 3H-etorphine or with the opiate antagonist 3H-diprenorphine, are solubilized with digitonin. The soluble digitonin extract is centrifuged in linear sucrose gradients. Under these conditions, we separate an agonist macromolecular complex and an antagonist macromolecular complex, the former sedimenting faster than does the latter. This difference in apparent molecular size might reflect an agonist-induced coupling between opiate receptor and other membrane components.

Animals↗
PubMed1982

[Multiple opiate receptor sites in the rabbit thalamus and cerebellum: preliminary characterization (author's transl)].

Inhibition of 3H-etorphine binding by D-Ala2, D-Leu5-enkephalin, a delta agonist and by morphiceptin, a mu agonist, reveals the existence of at least two classes of binding sites for the tritiated oviparine in membranes from the Rabbit thalamus and cerebellum. In the thalamus, approximately 50% of these sites appear to be mu receptor sites whereas the other half is neither of the mu nor of the delta subtype. In the cerebellum, at least 80% of the 3H-etorphine binding sites would belong to the mu subtype. This result may be related to the fact that the rabbit cerebellum contains appreciable quantities of methionine-enkephalin but little if any leucine-enkephalin.

Animals↗