Search PubMed⌕ Search

Biomedical subjects

P Nicolas

Publications and source records attributed to P Nicolas.

At least 181 records · Page 10Linked to original sources
PubMed1983

Regional distribution of the Mr 15,000 somatostatin precursor, somatostatin-28 and somatostatin-14 in the rat brain suggests a differential intracellular processing of the high molecular weight species.

Three different forms of immunoreactive somatostatin (Mr 15,000, 3,000 and 1,600) were immunologically detected in extracts made from six neural structures of the rat brain. The largest represents the proform, while the smaller were identified by high pressure liquid chromatography with bovine somatostatin-28 (S-28) and -14 (S-14) respectively. In each of the brain structures studied highly variable proportions of precursor, S-28 and S-14 were found. These observations provide suggestive evidence that the intracellular processing of the 15,000 Mr proform may occur differently in the various somatostatinergic pathways of the brain. They argue in favor of a biological role for the precursor in providing distinct relative proportions of S-14 and S-28 in specific rat brain regions.

Animals↗
PubMed1983

Synthesis and properties of dermorphin and an analog of beta-endorphin containing the dermorphin sequence.

Dermorphin (I) and [D-Ala2, Phe3, Gly4, Tyr5, Pro6]-beta c-EP (II) have been synthesized by the solid-phase method (beta c-EP, camel beta-endorphin). Positions 1 through 7 of II correspond to the sequence of I. Relative potencies of synthetic peptides in the mouse tail-flick test for analgesia by the intracerebroventricular route were: human beta-endorphin, 100; camel beta-endorphin, 164; I, 450; II, 440. The dermorphin was about 670 times more potent than morphine in the assay. Peptide II represents a rare instance where the enkephalin moiety of beta-endorphin has been altered to produce a more potent analgesic.

Amino Acid Sequence↗
PubMed1983

[Charnley type total hip replacement. Radiological technic of angular measurements of the acetabulum. Anteversion, inclination. Use of microcomputers].

A trigonometric method for studying the anteversion of the acetabular portion of Charnley's prosthesis involves the use of standing anteroposterior and lateral pelvic films. Although a statistical analysis of results has not been conducted, the method was proved to be valid in thirty or so Charnley type total hip replacements, confirmation being supplied by operative findings when repeat surgery became necessary.

Acetabulum↗
PubMed1982

Binding of neurohypophyseal peptides to neurophysin dimer promotes formation of compact and spherical complexes.

Previous hydrodynamic studies [Rholam, M., & Nicolas, P. (1981) Biochemistry 20, 5837-5843] have demonstrated that the dimerization of a neurophysin monomer (prolate ellipsoid with an axial ratio, due to asymmetry, of 5.2) results in a decreased asymmetry (axial ratio, due to asymmetry, of 3.6) as the consequence of a side-by-side association process. By a combination of hydrodynamic measurements, including the use of sedimentation velocity, viscometry, and fluorescence polarization spectroscopy, the influence of hormone binding on the shape and asymmetry properties of the neurophysin dimer was evaluated. The binding of ocytocin, vasopressin, and the tripeptide analogue of the N-terminal sequence of ocytocin, Cys(S-Me)-Tyr-Ile-NH2, results in an increase of S020,W and a decrease in both the reduced viscosity and rotational relaxation time of the bis-liganded dimeric species vs. the nonliganded form. The axial ratio (a/b) due to asymmetry of the ligand-bound dimers was found in each case to be equal to, or slightly greater than, 1.0, indicating a compact spherical shape (Stokes radius 21 A). The profound alteration on molecular dimensions observed upon ligand binding is shown to be the consequence of a ligand-induced conformational change and might explain the intradimeric binding sites positive cooperativity. It is tentatively proposed that the pseudospherical shape of the neurophysin-hormone complexes may enhance the stability of neurophysin and contribute to the prevention of leakage of neuropeptides through the membrane of neurosecretory granules. The data provide a remarkable example of a small protein with a high content in disulfide links and that undergoes conspicuous changes in conformation under the influence of nonapeptide, or tripeptide, ligands.

Binding Sites↗
PubMed1982

[Different phenotypes of non-photosynthetic (photo-) phenotypes in Euglena gracilis: frequency of production by ultraviolet irradiation].

In Euglena gracilis, pigment-less mutants appear spontaneously with a frequency of about 2-5 x 10(-3). Ultraviolet-irradiation increases the proportion of chlorophyll-less colonies to an upper limit where green colonies represent 4 x 10(-4) of the surviving ones. This limit indicate the occurrence of processes involving repair of the chloroplastic DNA. Most of the photosynthetic-deficient (phot-) mutants induced by ultraviolet irradiation are characterized by the presence of a reduced number of chloroplast DNA molecules showing deletions (phi class). Most of the phi- mutants present the phenotype phi- chlo- car-, where neither chlorophyll nor carotenoids are obvious; the phi- chlo- car+ mutants, devoid of chlorophyll but containing carotenoids, are obtained among the phi- strains with a frequency lower than 10(-3). The phot- mutants which belong to the cp- class are characterized by the maintenance of a great number of chloroplastic DNA molecules, where large deletions are absent; their occurrence after ultraviolet irradiation is low.

Animals↗
PubMed1982

Characterization of beta-endorphin binding protein (receptor) from rat brain membranes.

Rat brain membranes (RBM) bind beta-endorphin with high affinity and specificity. We report herein the identification of a high molecular weight beta-endorphin complex (receptor) in extracts of RBM preincubated with tritiated beta-endorphin, by using the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). Upon isoelectric focusing, this complex gives a single peak with an isoelectric point (+/- SEM) of 4.50 +/- 0.06. Sucrose density gradient experiments in H2O and 2H2O yield effective partial specific volume (v = 0.814 cm3/g and sedimentation constant s20,w = 15.6 S. Gel filtration yields an estimate of the hydrodynamic radius of 73 A. The corresponding frictional ratio of 1.12 is consistent with an elliptical spheroid with an axial ratio of 3.1-3.2. The molecular mass of the complex is estimated to be 690,000 daltons. The v of the complex is greater than that of CHAPS or most globular proteins.

Animals↗
PubMed1982

Beta-endorphin: replacement of tyrosine in position 27 by tryptophan increases analgesic potency--preparation and properties of the 2-nitrophenylsulfenyl derivative.

An analog of human beta-endorphin with tryptophan in position 27 has been synthetized by the solid-phase method. Bioassay of the analog showed that it had almost 4 times the analgesic potency of the parent hormone but only 68% of the opiate receptor-binding activity. The peptide is the most potent analgesic among the known synthetic analogs of beta-endorphin. The 2-nitrophenylsulfenyl derivative of the analog has been prepared and shown to have a lower analgesic potency and a higher opiate receptor-binding activity than the parent compound.

Amino Acid Sequence↗
PubMed1982

Beta-endorphin: opiate receptor binding activities of six naturally occurring beta-endorphin homologs studied by using tritiated human hormone and naloxone as primary ligands--effects of sodium ion.

Six naturally occurring homologs of beta-endorphin were tested for their potency in inhibiting the binding of [3H]naloxone and [3H]-beta h-endorphin either in the presence or in the absence of Na+. Sodium ion reduces inhibitory potency of these homologs against [3H]-beta h-endorphin and [3H]naloxone to about the same extent. The ratio of the IC50 obtained with Na+ to that obtained without Na+ is not highly correlated with analgesic potency. Very high (greater than 300) sodium ratios are observed with some homologs. A significant rank correlation was found between the ratio of the relative potency in displacing [3H]beta h-endorphin to the relative potency in analgesia and potency in inhibiting the binding of the pure antagonist naloxone.

Animals↗
PubMed1982

beta-Endorphin: analgesic and receptor binding activity of non-mammalian homologs.

Analgesic potencies of turkey, ostrich and des-acetyl salmon beta-endorphins have been measured in the tail-flick test and binding affinities determined by radio-receptor assay. The duration of analgesia and the slope of the dose-response curves generated by these peptides are similar to those elicited by mammalian beta-endorphins. This suggests that they act in vivo and in vitro on the same population of opiate receptors. The ratio of binding to analgesic potencies observed for these peptides varies nearly sixfold. Structure-activity analysis suggests that a basic side-chain at position 9 is required in order to produce a high opiate activity both in vivo and in vitro. A reexamination of the biological activities of camel beta-endorphin shows that the analgesic potency and binding affinity of this peptide are respectively 171 and 2.7 times higher than human beta-endorphin. His-27 and/or Gln-31 may contribute to this increased potency. The dissociation of radioreceptor binding affinity from analgesic potency in these naturally occurring beta-endorphin homologs suggests that either the conditions under which the binding assay is performed mask the true binding potency in the brain or that, once bound to the appropriate receptor, these homologs do not possess equal ability to produce biological effects.

Amino Acid Sequence↗
PubMed1982

beta-Endorphin: synthesis and properties of analogs modified in positions 8 and 31.

Four analogs of human beta-endorphin (beta h-EP) were synthesized by the solid-phase method: [Gln8,31]-beta h-EP(I), [Arg8,Gln31]-beta h-EP(II), [Ala8,Gln31]-beta h-EP (III), and [Val8, Gln31]-beta h-EP(IV). Radioreceptor binding assay with use of tritiated beta h-EP as primary ligand gave relative potencies as follows: beta h-EP, 100; I, 200;II, 150;III, 150;IV, 120. Relative potencies in an analgesic assay were: beta h-EP, 100; I,236;II, 254;III, 116;IV, 121. The side-chain of Glu-8 in beta h-EP can be replaced by a variety of structures without diminishing biological activity.

Amino Acid Sequence↗
PubMed1982

beta-Endorphin: synthesis and properties of human beta-endorphin-(1--28) and its analogs.

Three analogs of human beta-endorphin (beta h-EP) were synthesized by the solid-phage method: beta h-EP-(1--28) (I). [Gln8]-beta h-EP-(1--28) (II), and [D-Ala2, Gln8]-beta h-EP-(1--28) (III). Radioreceptor binding assay with use of tritiated beta h-EP as primary ligand gave relative potencies as follows: beta h-EP, 100; I, 85; II, 380; III, 146. Relative potencies in an analgesic assay were: beta h-EP; 100; I, 18; II, 36; III, 13.

Amino Acid Sequence↗
PubMed1982

Beta-Endorphin. Synthesis and properties of double-headed and related analogs.

A double-headed analog of human beta-endorphin (betah-EP), N,N'-bis (beta-endorphinyl)-cystine (II), has been synthesized by the solid-phase method, along with betah-EP-Cys(CH2CONH2)-OH (I) and [Tyr31]-betah-EP (III). Their relative potencies in a radioreceptor-binding assay were: betah-EP, 100; II, 235; I, 170; and III, 204. In the tail-flick test for analgesic activity their relative potencies were: betah-EP, 100; II, 86; I, 93; and III, 116.

Amino Acid Sequence↗
PubMed1981

Characterization of the 80,000 molecular weight form of neurophysin isolated from bovine neurohypophysis.

Partially purified immunoreactive species extracted from bovine posterior pituitary have been labeled with 125I and analyzed by immunoprecipitation with antineurophysin antibodies followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Under denaturing, but nonreducing conditions, a band of Mr = 80,000 was observed. This band corresponded to immunoreactive species detected by radioimmunoassay after chromatography of unlabeled material on a Sepharose CL-4B gel filtration column run in the presence of 6 M guanidine hydrochloride. Under nondenaturing conditions, this species behaved like molecules with an apparent Mr of 140,000 to 160,000. Electrophoretic analysis of the immunoprecipitated material showed that it contained an immunoreactive, single polypeptide chain of Mr = 80,000. Another immunoreactive species of similar molecular weight was also detected, apparently derived from the first one by peptide bond cleavage yielding two fragments of Mr = 68,000 and 10,000, respectively, held together by disulfide bridges. The Mr = 68,000 fragment had lost immunoprecipitability, although its peptide map was largely homologous to that or Mr = 80,000 polypeptide. The 10,000 piece was shown by radioimmunoassay and peptide analysis to be homologous to neurophysin.

Animals↗
PubMed1981

The chloroplast genome of bleached mutants of Euglena gracilis.

Bleached mutants of Euglena gracilis, traditionally thought to be completely deprived of chloroplast DNA, have been shown to contain a defective chloroplast genome, present at a very low copy number, and preferentially retaining ribosomal RNA genes. We propose to call these mutants phi-, because of their resemblance with the rho- mutants of yeast.

Chloroplasts↗