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R Buchet

Publications and source records attributed to R Buchet.

At least 19 recordsLinked to original sources
PubMed1995

Thermal and pH stabilities of alkaline phosphatase from bovine intestinal mucosa: a FTIR study.

The inactivation of alkaline phosphatase (AP) from bovine intestinal mucosa caused by lowering the p2H from 10.4 to 5.4 or by increasing the temperature from 25 degrees C to 70 degrees C were not followed by significant FTIR changes, indicating that the native conformation of AP was preserved under these conditions. Further decrease of p2H from 5.4 to 3.4 leaded to small infrared spectral changes of AP in the amide I' and amide II regions that were similar to the infrared spectral changes of AP induced by raising the temperature from 70 degrees C to 80 degrees C. The increase of temperature from 70 degrees C to 80 degrees C promoted the formation of intermolecular beta-sheets at the expense of some alpha-helix structures as evidenced by the appearance of the 1684 cm-1 and 1620 cm-1 component bands and the disappearance of the 1651-1657 cm-1 component band. This conformational change was followed by a sharp increase of the 2H/H exchange rate. CD spectra confirmed the FTIR results and were very sensitive to the variation of alpha-helix content while FTIR spectra were more receptive to the changes of beta-sheet structures.

Alkaline Phosphatase↗
PubMed1992

The effect of dicyclohexylcarbodiimide and cyclopiazonic acid on the difference FTIR spectra of sarcoplasmic reticulum induced by photolysis of caged-ATP and caged-Ca2+.

The photochemical release of Ca2+ from caged-Ca2+ in the absence of ATP, and the release of ATP from caged-ATP in the presence of Ca2+ induce characteristic difference FTIR spectra on rabbit sarcoplasmic reticulum that are related to the formation of Ca2-E1 and E approximately P intermediates of the Ca(2+)-ATPase, respectively. Dicyclohexylcarbodiimide (10 nmol/mg protein) abolished both the Ca(2+)-and ATP-induced difference FTIR spectra parallel with inhibition of ATPase activity. Cyclopiazonic acid (50 nmol/mg protein) inhibited the Ca(2+)-induced difference spectrum measured in the absence of ATP, but had no significant effect on the ATP-induced difference spectrum measured in the presence of 1 mM Ca2+. The dog kidney Na+,K(+)-ATPase did not give significant difference spectrum after photolysis of caged-ATP in Ca(2+)-free media containing 90 mM Na+ and 10 mM K+, with or without ouabain. We propose that both the Ca2+ and the ATP-induced difference FTIR spectra of the Ca(2+)-ATPase reflect the occupancy of the high-affinity Ca2+ transport site of the enzyme.

Adenosine Triphosphatases↗
PubMed1991

Ca2+ release from caged-Ca2+ alters the FTIR spectrum of sarcoplasmic reticulum.

Light-induced Ca2+ release from the Ca2+ complex of Nitr-5 altered the FTIR spectra of sarcoplasmic reticulum vesicles and purified Ca(2+)-ATPase preparations. The principal changes seen in difference spectra obtained after and before illumination in the presence of Nitr-5.Ca2+ consisted of an increase in absorbance at 1663 and 1676 cm-1 and a decrease in absorbance at 1653 cm-1. The light-induced changes in FTIR spectra were prevented by vanadate or EGTA, indicating that they were associated with the formation of Ca2E1 enzyme intermediate. Other light-induced changes in the FTIR spectra at 1600-1250 cm-1 were not clearly related to the sarcoplasmic reticulum, and were attributed to photolysis of Nitr-5. The difference absorbance bands are narrow, suggesting that they originate from changes in side chain vibrations, although some changes in secondary structures may also contribute.

Biological Transport↗
PubMed1991

Polarized infrared attenuated total reflectance spectroscopy of the Ca(2+)-ATPase of sarcoplasmic reticulum.

The mean orientations of the transition dipole moments associated with vibrational modes of the proteins and phospholipids of sarcoplasmic reticulum were determined on dry and hydrated membrane multilayers deposited on germanium or zinc selenide crystals, using polarized infrared attenuated total reflectance spectroscopy (P-IR-ATR). For preservation of the enzymatic activity of the Ca(2+)-ATPase the films were prepared from solutions containing 0.05 M KCl, 5 mM imidazole (pH 7.4), 0.5 mM MgCl2, 1-10 mM trehalose and dithiothreitol. The anisotropy was highest in dry films containing congruent to 7.5 micrograms protein/cm2, and decreased with increasing membrane thickness or hydration. The dichroic ratio of the CH2 vibrations (2923 cm-1) of extracted sarcoplasmic reticulum phospholipids on Ge plate was 1.56, compared with a dichroic ratio of 1.68 obtained on dry films of whole sarcoplasmic reticulum. The dichroic ratios of the amide I band (1650 cm-1) of the Ca(2+)-ATPase in the Ca2-E1 state and in the EGTA and vanadate stabilized E2-V state were nearly identical (1.60 vs. 1.62). The dichroism of the amide I, amide II and lipid CH2 vibrations was not affected by changes in the concentration of KCl (25-100 mM) or Ca2+ (approximately equal to 10(-8)-10(-4) M) and by the addition of vanadate (1 mM) or Pi (5 mM) in a calcium-free medium containing 0.5 mM EGTA. The dichroic ratio of the C-C (1033 cm-1) or CO stretching band (1046 cm-1) of trehalose incorporated into SR films was 1.2 on Ge plate; this corresponds to a mean angle of approximately 70 degrees between the plane of the trehalose ring and the normal of the film plane, suggesting that the trehalose molecules are surprisingly well oriented in the polar headgroup region of the phospholipids. The orientation of the trehalose was not affected by the presence of Ca(2+)-ATPase.

Calcium-Transporting ATPases↗
PubMed1990

Emerging views on the structure and dynamics of the Ca2(+)-ATPase in sarcoplasmic reticulum.

The ATP-dependent Ca2+ transport in sarcoplasmic reticulum involves transitions between several structural states of the Ca2(+)-ATPase, that occur without major changes in the secondary structure. The rates of these transitions are modulated by the lipid environment and by interactions between ATPase molecules. Although the Ca2(+)-ATPase restricts the rotational mobility of a population of lipids, there is no evidence for specific interaction of the Ca2(+)-ATPase with phospholipids. Fluorescence polarization and energy transfer (FET) studies, using site specific fluorescent indicators, combined with crystallographic, immunological and chemical modification data, yielded a structural model of Ca2(+)-ATPase in which the binding sites of Ca2+ and ATP are tentatively identified. The temperature dependence of FET between fluorophores attached to different regions of the ATPase indicates the existence of 'rigid' and 'flexible' regions within the molecule characterized, by different degrees of thermally induced structural fluctuations.

Animals↗
PubMed1990

Pressure effects on sarcoplasmic reticulum: a Fourier transform infrared spectroscopic study.

The Ca2(+)-ATPase of sarcoplasmic reticulum is irreversibly inactivated by exposure to 1.5-2.0 kbar pressure for 30-60 min in a Ca2(+)-free medium; mono- or decavanadate (5 mM) or to a lesser extent Ca2+ (2-20 mM) protect against inactivation (Varga et al. (1986) J. Biol. Chem. 261, 13943-13956). The structural basis of these effects was analyzed by FTIR spectroscopy of sarcoplasmic reticulum in 2H2O medium. The inactivation of the Ca2(+)-ATPase at 1.5-2.0 kbar pressure in a Ca2(+)-free medium was accompanied by changes in the Amide II region of the spectrum (1550 cm-1), that are consistent with increased hydrogen-deuterium (H-2H) exchange, and by the enhancement of a band at 1630 cm-1 in the Amide I region, that is attributed to an increase in beta sheet. The frequency of the peak of the Amide I band shifted from about 1648 cm-1 at atmospheric pressure to 1642 cm-1 at approximately equal to 12.5 kbar pressure, suggesting a decrease in alpha helix, and an increase in beta and/or random coil structures. Upon releasing the pressure, the shift of the Amide I band was partially reversed. Vanadate (5 mM), and to a lesser extent Ca2+ (2-20 mM), protected the Ca2(+)-ATPase against pressure-induced changes both in the Amide I and Amide II regions of the spectrum, together with protection of ATPase activity. These observations establish a correlation between the conformation of the Ca2(+)-ATPase and its sensitivity to pressure. The involvement of the ATP binding domain of the Ca2(+)-ATPase in the pressure-induced structural changes is suggested by the decreased polarization of fluorescence of fluorescein 5'-isothiocyanate covalently attached to the enzyme.

Animals↗
PubMed1989

Correlation of structure and function in the Ca2+-ATPase of sarcoplasmic reticulum: a Fourier transform infrared spectroscopy (FTIR) study on the effects of dimethyl sulfoxide and urea.

The effect of dimethyl sulfoxide (DMSO) on the structure of sarcoplasmic reticulum was analyzed by Fourier transform infrared (FTIR) and fluorescence spectroscopy. Exposure of sarcoplasmic reticulum vesicles to 35% DMSO (v/v) at 2 degrees C for several hours in a D2O medium produced no significant change in the phospholipid and protein Amide I regions of the FTIR spectra, but the intensity of the Amide II band decreased, presumably due to proton/deuterium exchange. At 40% to 60% DMSO concentration a shoulder appeared in the FTIR spectra at 1630 cm-1, that is attributed to the formation of new beta or random coil structures; irreversible loss of ATPase activity accompanied this change. At 70% DMSO concentration the intensity of the main Amide I band at 1639 cm-1 decreased and a new band appeared at 1622 cm-1, together with a shoulder at 1682 cm-1. These changes indicate an abrupt shift in the conformational equilibrium of Ca2+-ATPase from alpha to beta structure or to a new structure characterized by weaker hydrogen bonding. Decrease of ionization of aspartate and glutamate carboxyl groups in the presence of DMSO may also contribute to the change in intensity at 1622 cm-1. The changes were partially reversed upon removal of DMSO. Exposure of sarcoplasmic reticulum vesicles to 1.5 kbar pressure for 1 h at 2 degrees C in an EGTA-containing (low Ca2+) medium causes irreversible loss of ATPase activity, with the appearance of new beta structure, and abolition of the Ca2+-induced fluorescence response of FITC covalently bound to the Ca2+-ATPase; DMSO (35%) stabilized the Ca2+-ATPase against pressure-induced changes in structure and enzymatic activity, while urea (0.8 M) had the opposite effect.

Animals↗
PubMed1989

[Paralysis of the serratus anterior muscle. A misleading trap in pulmonary radiology].

Paralysis of the serratus anterior muscle is an infrequent event, usually caused by an injury, and has not previously been reported in the radiologic literature. Diagnosis rests on clinical findings that include limitation of forward flexion and, to a lesser degree, abduction. The chest film may show a misleading parietal density projecting over the upper lobe. Medical treatment is usually adequate and prognosis is good.

Adult↗
PubMed1989

[Pleural fibroma. Development of diagnostic methods and current anatomo-pathologic aspects. Apropos of 2 cases].

Pleural fibroma is a rare benign primary pleural tumour which has a favourable prognosis after surgical resection. Preoperatively, the diagnosis of the tumour of pleural origin can be made by means of modern imaging techniques, particularly computed tomography. However, there are no formal computed tomography or magnetic resonance imaging criteria allowing a precise characterisation of the tissues. The definitive diagnosis of pleural fibroma can only be based on histological examination of the entire surgical specimen.

Diagnosis, Differential↗
PubMed1988

Dielectric relaxation spectroscopy on dimyristoylphosphatidylcholine-packaged gramicidin A.

The complex permittivities of aqueous suspensions of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and of DMPC packaged gramicidin A' (DMPC-GA) have been determined over the frequency range of 1 MHz to 1 GHz and the temperature range of 0-60 degrees C. A dielectric relaxation/loss has been observed at about 66 MHz for the DMPC suspension (30 degrees C) and at about 57 MHz for the DMPC-GA suspension (30 degrees C). This dielectric relaxation/loss has been attributed to the rotational mobility of the zwitterionic group of DMPC. The temperature dependence (from 60 degrees C to 0 degrees C) of this dispersion/absorption process of the DMPC suspension indicates a sharp reduction of the dielectric relaxation at about 20 degrees C. This dielectric change is related to the conversions of shape and structure of bilayer aggregates. This sharp reduction of the dielectric relaxation disappears or broadens when GA is incorporated into the DMPC aqueous suspension. The interpretation of these results is that the GA addition into the DMPC aqueous suspension induces a small decrease of the rotational mobility of the zwitterionic group above the lipid phase transition, and a small increase of the rotational mobility of the zwitterionic group below the lipid phase transition.

Dimyristoylphosphatidylcholine↗
PubMed1988

Dielectric spectroscopy of L-alpha-lysolecithin-packaged gramicidin A.

The complex permittivities of L-alpha-lysolecithin in the absence and presence of the gramicidin A ion channel were measured over the temperature range 0-60 degrees C and over the frequency range 1-1000 MHz. One dielectric relaxation/loss has been observed. It is located at 103.3 MHz (1.54 ns) for a micellar 0.4 M L-alpha-lysolecithin solution at 20 degrees C, whereas it is shifted to 71.7 MHz (2.22 ns) for a lamellar L-alpha-lysolecithin-gramicidin A aqueous solution (0.4 M L-alpha-lysolecithin, 0.0308 M gramicidin A) at 20 degrees C. The dielectric relaxation decreases and the relaxation time increases when gramicidin A is incorporated into L-alpha-lysolecithin. These dielectric changes are related, in part, to the micellar-to-lamellar lipid phase transition induced by the incorporation of gramicidin A into lysolecithin. We suggest that the diffuse rotational motion of the polar head group of L-alpha-lysolecithin contributes to the dielectric relaxation/loss at around 100 MHz.

Electrochemistry↗
PubMed1986

Hydrogen bond equilibrium constants for the complexes of benzotriazole and some nucleoside derivatives. A near infrared study.

Approximate hydrogen bond association constants were determined by near infrared spectroscopy for pairs formed by benzotriazole and a number of nucleoside derivatives. The molecule of benzotriazole forms, in chloroform, hydrogen bonds with inosine, uridine and adenosine derivatives. The order of decreasing association constants for complexes formed by benzotriazole and uridine or inosine derivatives is the opposite of the one observed for pairs formed by adenosine and uridine or inosine derivatives.

Chloroform↗
PubMed1985

Infrared spectroscopic studies on gramicidin ion-channels: relation to the mechanisms of anesthesia.

Fourier transform infrared spectroscopic studies are reported on gramicidin ion-channels in phospholipid bilayers and the effects on the spectra of the anesthetics and related compounds (methoxyflurane, halothane, chloroform, carbon tetrachloride, n-pentane and n-decane) have been determined. The addition of anesthetics containing the 'acidic hydrogen' caused unique changes particularly on the amide I bands at 1639 cm-1 and 1670 cm-1. The 1639 cm-1 band became more intense while the intensity near 1670 cm-1 decreased dramatically. These effects were not observed with carbon tetrachloride, n-pentane and n-decane. The 1670 cm-1 band is interpreted as arising from the carbonyls involved in the head-to-head hydrogen-bonded dimerization where the relationship between chains is analogous to that of the antiparallel beta-pleated sheet structure and the anesthetics with 'acidic hydrogens' are considered to disrupt the hydrogen-bonded dimerization by competitive hydrogen bonding to the carbonyls at the head-to-head junction. As the dimer-monomer equilibrium is the 'on-off' mechanism for gramicidin ion-channel conductance, the results are considered in terms of the mechanism of action of anesthetics and are taken to suggest, for certain anesthetics, a hydrogen-bonding role to protein ion-channel components.

Anesthesia↗
PubMed1985

The effect of anesthetics on hydrogen bonds. An infrared study at low anesthetic concentrations.

It is shown that a striking parallelism exists between the anesthetic potency of general halocarbon anesthetics and their influence on the hydrogen bond association constants in N-H...O=C type hydrogen bonds, important for shaping the ion channels. It is further shown that the effect of potent anesthetics (which contain an acidic hydrogen) on the free/associated ratio in such hydrogen bonds is still significant at clinical anesthetic concentrations. It is argued that the results are in keeping with a pluralistic theory of anesthesia based on both hydrophobic and polar interactions.

Acetamides↗
PubMed1984

Hydrogen bond equilibrium constants of some unusual nucleotide base pairs.

Approximate hydrogen bond association constants were determined for base pairs formed by an adenine derivative and a number of unusual pyrimidine bases. A series is found in which the H-bond strength in the base-pairs varies. In certain cases the H-bond equilibrium constant is larger than in the adenine-thymine pair. Inosine derivatives seem to have a non-negligible chance of replacing guanosine in the guanosine-cytosine pair. Infrared, near-infrared (overtone) and NMR spectra were used to determine the equilibrium constants.

Base Composition↗