Search PubMed⌕ Search

Biomedical subjects

J Breton

Publications and source records attributed to J Breton.

At least 91 records · Page 5Linked to original sources
PubMed1993

Effect of selective phosphodiesterase type IV inhibitor, rolipram, on fluid and cellular phases of inflammatory response.

The antiinflammatory activity of rolipram, a selective inhibitor of the cyclic AMP-specific phosphodiesterase (PDE IV), was studied. Rolipram did not inhibit 5-lipoxygenase activity but did inhibit human monocyte production of leukotriene B4 (LTB4, IC50 3.5 microM). Likewise, murine mast cell release of leukotriene C4 and histamine was inhibited. In vivo, rolipram inhibited arachidonic acid-induced inflammation in the mouse, while the low Km-cyclic-GMP PDE inhibitor, zaprinast, did not inhibit. Rolipram had a modest effect on LTB4 production in the mouse, but markedly reduced LTB4-induced PMN infiltration. Beta-adrenergic receptor activation of adenylate cyclase was important for rolipram antiinflammatory activity since beta blockade abrogated arachidonic acid-induced inflammation. Thus, the antiinflammatory profile of rolipram is novel and may result from inhibition of PMN function and perhaps vasoactive amine release and leukotriene biosynthesis. These actions may be dependent upon endogenous beta-adrenergic activity and are likely mediated through inhibition of PDE IV.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1993

Use of a continuous assay of oxygen consumption to evaluate the pharmacology of 5-lipoxygenase inhibitors.

A variety of assay systems have been utilized to evaluate the inhibition of the key enzyme in leukotriene (LT) biosynthesis, 5-lipoxygenase (5-LO). We have developed an assay utilizing a cytosolic preparation of 5-LO from rat basophilic leukemia (RBL-1) cells. Enzyme activity was monitored by continuous measurement of oxygen consumption. High performance liquid chromatography (HPLC) analysis of products showed exclusive generation of 5-LO products. The assay proved useful for the evaluation of a variety of chemical classes of lipoxygenase inhibitors and clearly differentiated those compounds which extended the lag phase (e.g. A-64077) as opposed to the propagation phase of the enzyme activity (e.g. SK & F 105561). The data generated were in reasonable agreement with results from the assay of isolated human monocyte 5-LO and, with the exception of compounds which appear to have a significant effect on 5-LO translocation (e.g. MK-886 and Wy-49 232), inhibition of LT production by intact monocytes. This assay system proved to be a convenient and informative method to analyze inhibition of 5-LO activity.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1993

Why does the light-gradient photovoltage from photosynthetic organelles show a wavelength-dependent polarity?

The light-gradient photovoltage from photosynthetic organisms and organelles is thought to arise from the primary charge separation in the reaction centers. The current explanation of the effect is the stronger excitation of the membrane side of a vesicle facing the light source than the one on the opposite side. Together with the known orientation of reaction centers, this explanation predicts unequivocally the polarity of the photovoltage. However, a polarity opposite to the one expected has often been reported. A dependence of the polarity on the wavelength has been published but no explanation was given (Gräber, P., and H.-W. Trissl. 1981. FEBS Lett. 123:95-99). Here we report on a theoretical treatment of light propagation and interference in pigmented and nonpigmented multilayers. A model calculation is carried out for a pair of membranes, demonstrating the wavelength-dependent light distribution as well as the relative photovoltage and its polarity. When the membranes contain no chromophores or when the absorption coefficient is low, the predicted polarity to that expected from a simple macroscopic absorption behavior. The model is tested by comparing new photovoltage data obtained at 532 nm as well as in the blue and red absorption bands of chlorophyll in chloroplasts. It is concluded that outside the main absorption bands the amplitude and polarity of the photovoltage is determined by the ratio of the refractive indices of the membrane and the medium.

Biophysical Phenomena↗
PubMed1993

The major intrinsic light-harvesting protein of Amphidinium: characterization and relation to other light-harvesting proteins.

A major light-harvesting complex (LHC) has been obtained from thylakoids of Amphidinium carterae solubilized with digitonin or decylmaltoside and separated by sucrose-gradient centrifugation. The digitonin-LHC forms a dark brown band at approximately 17% sucrose and the decylmaltoside LHC one at approximately 7% sucrose. Excellent energy transfer is retained from chlorophyll c and carotenoid to chlorophyll a. Absorbance and fluorescence excitation spectra show the existence of two major forms of chlorophyll c, one absorbing at 634 nm and the other at 649 nm. Linear dichroism spectra show the Qy transition of both forms of chlorophyll c to be aligned at < 35 degrees to the membrane plane. On sodium dodecylsulfate polyacrylamide gels the complex resolves as a single band of 19 kDa. A partial amino acid sequence shows the N-terminus to be unblocked but modified; there is a persistent ambiguity of Ser/Asn at residue 4 and evidence for multiple but very similar polypeptides within the 19 kDa band. The peptide has strong identity with the N-terminal regions of LHC from Phaeodactylum and Pavlova and LHC 1 of higher plants. Antibodies to the 19 kDa peptide react weakly with LHC of brown algae, diatoms and Prymnesiophytes but not with those of higher plants or Cryptophytes.

Amino Acid Sequence↗
PubMed1992

Molecular changes following oxidoreduction of cytochrome b559 characterized by Fourier transform infrared difference spectroscopy and electron paramagnetic resonance: photooxidation in photosystem II and electrochemistry of isolated cytochrome b559 and iron protoporphyrin IX-bisimidazole model compounds.

The vibrational infrared absorption changes associated with the oxidation of cytochrome b559 (Cyt b559) have been characterized. In photosystem II (PS II) enriched membranes, low-potential (LP) and high-potential (HP) Cyt b559 were investigated by light-induced FTIR difference spectroscopy. The redox transition of isolated Cyt b559 is characterized by protein electrochemistry. On the basis of a model of the assembly of Cyt b559 with the two axial Fe ligands being histidine residues of two distinct polypeptides, each forming a transmembrane alpha-helix [Cramer, W.A., Theg, S.M., & Widger, W.R. (1986) Photosynth. Res. 10, 393-403], the bisimidazole and bismethylimidazole complexes of Fe protoporphyrin IX were electrochemically oxidized and reduced to detect the IR oxidation markers of the heme and its two axial ligands. Major bands at 1674/1553, 1535, and 1240 cm-1 are tentatively assigned to nu 37 (CaCm), nu 38-(CbCb) and delta (CmH) modes, respectively; other bands at 1626, 1613, 1455, 1415, and 1337 cm-1 are assigned to porphyrin skeletal and vinyl modes. Modes at 1103 and 1075/1066 cm-1 are assigned to the 4-methylimidazole and imidazole ligands, respectively. For the isolated Cyt b559, it is shown that both the heme (at 1556-1535, 1337, and 1239 cm-1), the histidine ligands at 1104 cm-1 and the protein (between 1600 and 1700 cm-1 and at 1545 cm-1) are affected by the charge stabilization. The excellent agreement between model compounds and isolated Cyt b559 reinforces the validity of the model of a heme iron coordinated to two histidine residues for Cyt b559. A differential signal at 1656/1641 cm-1 is assigned to peptide C = O mode(s). We speculate that this signal reflects the change in strength of a hydrogen bond formed between the histidine ligand(s) and the polypeptide backbone upon oxidoreduction of the cytochrome. In PS II membranes, the signals characteristic of Cyt b559 photooxidation are found at 1660/1652 and 1625 cm-1, for both the high- and low-potential forms. The differences observed in the amplitude of the 1660/1652-cm-1 band, at 1700 and 1530-1510 cm-1 in the light-induced FTIR difference spectra of Cyt b559 HP and LP, show that the mechanisms of heme oxidation in vivo imply different molecular processes for the two forms Cyt b559 HP and LP.

Cold Temperature↗
PubMed1992

Probing the primary donor environment in the histidineM200-->leucine and histidineL173-->leucine heterodimer mutants of Rhodobacter capsulatus by light-induced Fourier transform infrared difference spectroscopy.

Light-induced P+QB-/PQB FTIR difference spectra of reaction centers (RCs) have been obtained from chromatophores lacking light-harvesting B800-850 antenna for Rhodobacter capsulatus wild type (WT) and for the two mutants HisM200-->Leu and HisL173-->Leu. The primary donor (P) in both mutants consists of a bacteriochlorophyll-bacteriopheophytin heterodimer. The most prominent difference between the WT and the mutant spectra is in the 1600-1200-cm-1 region. The WT spectrum displays large positive bands at approximately 1290, 1500-1430, and 1580-1530 cm-1. These three bands are either small or altogether absent in the heterodimer spectra. In addition, both heterodimer spectra compare well with the electrochemically generated BChla+/BChla spectrum [Mäntele, W.G., Wollenweber, A. M., Nabedryk, E., & Breton, J. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 8468-8472]. These observations indicate that the positive charge is localized on the monomeric BChl in the heterodimers. The overall shape of the ester and keto C = O signals in the BChla+/BChla spectrum is maintained in the in situ spectra although significant differences are observed in the frequency, width, and splitting of the bands. The shape of the signal at 1757/1744 cm-1 in HisL173-->Leu is comparable to the 1751/1737-cm-1 signal of BChla+/BChla in tetrahydrofuran, indicating a free 10a ester C = O of PM in HisL173-->Leu. The reduced amplitude of the negative 1740-cm-1 feature in both HisM200-->Leu and WT spectra suggests a hydrogen-bonded 10a ester C = O for PL.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriochlorophylls↗
PubMed1992

A new infrared electronic transition of the oxidized primary electron donor in bacterial reaction centers: a way to assess resonance interactions between the bacteriochlorophylls.

The primary electron donor in the reaction center of purple photosynthetic bacteria consists of a pair of bacteriochlorophylls (PL and PM). The oxidized dimer (P+) is expected to have an absorption band in the mid-IR, whose energy and dipole strength depend in part on the resonance interactions between the two bacteriochlorophylls. A broad absorption band with the predicted properties was found in a previously unexplored region of the spectrum, centered near 2600 cm-1 in reaction centers of Rhodobacter sphaeroides and several other species of bacteria that contain bacteriochlorophyll a, and near 2750 cm-1 in Rhodopseudomonas viridis. The band is not seen in the absorption spectrum of the monomeric bacteriochlorophyll cation in solution, and it is missing or much diminished in the reaction centers of bacterial mutants that have a bacteriopheophytin in place of either PL or PM. With the aid of a relatively simple quantum mechanical model, the measured transition energy and dipole strength of the band can be used to solve for the resonance interaction matrix element that causes an electron to move back and forth between PL and PM, and also for the energy difference between states in which a positive charge is localized on either PL or PM. (The absorption band can be viewed as representing a transition between supermolecular eigenstates that are obtained by mixing these basis states.) The values of the matrix element obtained in this way agree reasonably well with values calculated by using semiempirical atomic resonance integrals and the reaction center crystal structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriochlorophylls↗
PubMed1992

Time-resolved infrared spectroscopy of electron transfer in bacterial photosynthetic reaction centers: dynamics of binding and interaction upon QA and QB reduction.

Light-induced forward electron transfer in the bacterial photosynthetic reaction center from Rhodobacter sphaeroides was investigated by time-resolved infrared spectroscopy. Using a highly sensitive kinetic photometer based on a tunable IR diode laser source [Mäntele, W., Hienerwadel, R., Lenz, F., Riedel, W. J., Grisar, R., & Tacke, M. (1990a) Spectrosc. Int. 2, 29-35], molecular processes concomitant with electron-transfer reactions were studied in the microsecond-to-second time scale. Infrared (IR) signals in the 1780-1430-cm-1 spectral region, appearing within the instrument time resolution of about 0.5 microseconds, could be assigned to molecular changes of the primary electron donor upon formation of a radical cation and to modes of the primary quinone electron acceptor QA and its environment upon formation of QA-. These IR signals are consistent with steady-state FTIR difference spectra of the P+Q- formation [Mäntele, W., Nabedryk, E., Tavitian, B. A., Kreutz, W., & Breton, J. (1985) FEBS Lett. 187, 227-232; Mäntele, W., Wollenweber, A., Nabedryk, E., & Breton, J. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 8468-8472; Nabedryk, E., Bagley, K. A., Thibodeau, D. L., Bauscher, M., Mäntele, W., & Breton, J. (1990) FEBS Lett. 266, 59-62] and with time-resolved FTIR studies [Thibodeau, D. L., Nabedryk, E., Hienerwadel, R., Lenz, F., Mäntele, W., & Breton, J. (1990) Biochim. Biophys. Acta 1020, 253-259]. At given wavenumbers, kinetic components with a half-time of approximately 120 microseconds were observed and attributed to QA----QB electron transfer. The time-resolved IR signals, in contrast to steady-state experiments where full protein relaxation after electron transfer can occur, allow us to follow directly the modes of QA and QB and their protein environment under conditions of forward electron transfer. Apart from signals attributed to the primary electron donor, signals are proposed to arise not only from the C = O and C = C vibrational modes of the neutral quinones and from the C-O and C-C vibrations of their semiquinone anion form but also from amino acid groups forming their binding sites. Some of the signals appearing with the instrument rise time as well as the transient 120-microseconds signals are interpreted in terms of binding and interaction of the primary and secondary quinone electron acceptor in the Rb. sphaeroides reaction center and of the conformational changes in their binding site.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding Sites↗
PubMed1992

Femtosecond spectral evolution of the excited state of bacterial reaction centers at 10 K.

The femtosecond spectral evolution of reaction centers of Rhodobacter sphaeroides R-26 was studied at 10 K. Transient spectra in the near infrared region, obtained with 45-fs pulses (pump pulses centered at 870 nm and continuum probe pulses), were analyzed with associated kinetics at specific wavelengths. The t = 0-fs transient spectrum is very rich in structure; it contains separate induced bands at 807 and 796 nm and a bleaching near 760 nm, reflecting strong changes in interaction between all pigments upon formation of the excited state. A complex spectral evolution in the 800-nm region, most notably the bleaching of the 796-nm band, takes place within a few hundred femtosecond--i.e., on a time scale much faster than electron transfer from the primary donor P to the bacteriopheophytin acceptor HL. The remarkable initial spectral features and their evolution are presumably related to the presence of HL, as they were not observed in the DLL mutant of Rhodobacter capsulatus, which lacks this pigment. A simple linear reaction scheme with an intermediate state cannot account for our data; the initial spectral evolution must reflect relaxation processes within the excited state. The importance for primary photochemistry of long distance interactions in the reaction center is discussed.

Cold Temperature↗
PubMed1991

Photooxidation of high-potential (c559, c556) and low-potential (c552) hemes in the cytochrome subunit of Rhodopseudomonas viridis reaction center. Characterization by FTIR spectroscopy.

The photooxidation of c559, c556 and c552 hemes in Rhodopseudomonas viridis cytochrome has been characterized by light-induced FTIR difference spectroscopy. Apart from the common features at 1659 cm-1 and 1561/1551 cm-1 which could arise from one (or possibly two) peptide bond(s), no evidence for major structural rearrangement of the polypeptide backbone was observed. A significant difference with respect to redox-induced FTIR spectra of cytochrome c is the absence of the Tyr marker at 1514/1518 cm-1 in Rps. viridis cytochrome, indicating that the localized shift of a Tyr side chain observed between ferro- and ferri-cytochrome c does not occur in Rps. viridis cytochrome.

Cytochrome c Group↗
PubMed1991

Direct observation of vibrational coherence in bacterial reaction centers using femtosecond absorption spectroscopy.

It is shown that vibrational coherence modulates the femtosecond kinetics of stimulated emission and absorption of reaction centers of purple bacteria. In the DLL mutant of Rhodobacter capsulatus, which lacks the bacteriopheophytin electron acceptor, oscillations with periods of approximately 500 fs and possibly also of approximately 2 ps were observed, which are associated with formation of the excited state. The kinetics, which reflect primary processes in Rhodobacter sphaeroides R-26, were modulated by oscillations with a period of approximately 700 fs at 796 nm and approximately 2 ps at 930 nm. In the latter case, at 930 nm, where the stimulated emission of the excited state, P*, is probed, oscillations could only be resolved when a sufficiently narrow (10 nm) and concomitantly long pump pulse was used. This may indicate that the potential energy surface of the excited state is anharmonic or that low-frequency oscillations are masked when higher frequency modes are also coherently excited, or both. The possibility is discussed that the primary charge separation may be a coherent and adiabatic process coupled to low-frequency vibrational modes.

Bacterial Chromatophores↗
PubMed1991

Kinetic properties of the acceptor quinone complex in Rhodopseudomonas viridis.

The kinetics of electron transfer from the primary (QA) to the secondary (QB) quinone acceptor in whole cells and chromatophores of Rhodopseudomonas viridis was studied as a function of the redox state of QB and of pH by using a photovoltage technique. Under conditions where QB was oxidized, the reoxidation of QA- was found to be essentially monophasic and independent of pH with a half-time of about 20 microseconds. When QB was reduced to the semiquinone form by a preflash, the reoxidation of QA- was slowed down showing a half-time between 40 and 80 microseconds at pH less than or equal to 9. Above pH 9, the rate of the second electron transfer decreased nearly one order of magnitude per pH unit. After a further preflash, the fast and pH-independent kinetics of QA- reoxidation was essentially restored. The concentration of QA still reduced 100 microseconds after its complete reduction by a flash showed distinct binary oscillations as a function of the number of preflashes, confirming the interpretation that the electron-transfer rate depends on the redox state of QB. After addition of o-phenanthroline, the reoxidation of QA- is slowed down to the time range of seconds as expected for a back-reaction with oxidized cytochrome. Under conditions where inhibitors of the electron transfer between the quinones fail to block this reaction in a fraction of the reaction centers due to the presence of the extremely stable and strongly bound semiquinone, QB-, these reaction centers show a slow electron transfer on the first flash and a fast one on the second, i.e., an out-of-phase oscillation.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzoquinones↗
PubMed1991

Probing the secondary quinone (QB) environment in photosynthetic bacterial reaction centers by light-induced FTIR difference spectroscopy.

The photoreduction of the secondary electron acceptor, QB, has been characterized by light-induced Fourier transform infrared difference spectroscopy of Rb. sphaeroides and Rp. viridis reaction centers. The reaction centers were supplemented with ubiquinone (UQ10 or UQ0). The QB- state was generated either by continuous illumination at very low intensity or by single flash in the presence of redox compounds which rapidly reduce the photooxidized primary electron donor P+. This approach yields spectra free from P and P+ contributions making possible the study of the microenvironment of QB and QB-. Assignments are proposed for the C...O vibration of QB- and tentatively for the C = O and C = C vibrations of QB.

Benzoquinones↗
PubMed1991

Pharmacology of the pyrroloimidazole, SK&F 105809--I. Inhibition of inflammatory cytokine production and of 5-lipoxygenase- and cyclooxygenase-mediated metabolism of arachidonic acid.

SK&F 105809 [2-(4- methylsulfinylphenyl)-3-(4-pyridyl)-6,7-dihydro-[5H]-pyrrolo[1,2- a] imidazole] was determined to be a prodrug for the sulfide metabolite SK&F 105561 [2-(4- methylthiophenyl)-3-(4-pyridyl)-6,7-dihydro-[5H]-pyrrolo[1,2-a] imidazole] which inhibited interleukin-1 (IL-1) production in vitro and both 5-lipoxygenase (5-LO) and prostaglandin H (PGH) synthase activities in vitro and ex vivo. SK&F 105561 inhibited partially purified 5-LO with a half-maximal concentration (IC50) of 3 microM. This inhibition was reversible, independent of preincubation time, and dependent on the concentration of the substrate arachidonic acid. SK&F 105561 also inhibited purified PGH synthase with the potency dependent on the level of peroxidase activity. The IC50 was 100 microM in the absence of peroxidase activity, whereas an IC50 of 3 microM was observed in the presence of peroxidase activity. Using human monocytes, SK&F 105561 inhibited A23187-stimulated prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) production with IC50 values of 0.1 and 2 microM, respectively. In addition, IL-1 production by lipopolysaccharide-stimulated human monocytes was also inhibited (IC50 2 microM). Oral administration of SK&F 105809 to rats resulted in a dose-related generation of SK&F 105561 and in the inhibition of thromboxane B2 and LTB4 production ex vivo with a half-maximal dose (ED50) of 15 and 60 mg/kg, respectively. SK&F 105561 showed weak inhibitory activity on 12-lipoxygenase with an IC50 of greater than 200 microM. Neither SK&F 105561 nor SK&F 105809 inhibited the stimulated-turnover of arachidonic acid-containing phospholipids in human monocytes or the activity of cell-free phospholipases A2 and C. Moreover, neither SK&F 105561 nor SK&F 105809 antagonized the binding of LTB4 or leukotriene D4 to membrane receptors. From these results, SK&F 105561, the active principle of SK&F 105809, acts as an inhibitor of both inflammatory cytokine and eicosanoid production.

Animals↗
PubMed1991

Orientation and linear dichroism of Mastigocladus laminosus phycocyanin trimer and Nostoc sp. phycocyanin dodecamer in stretched poly(vinyl alcohol) films.

The linear dichroism (LD) spectra of the C-phycocyanin (C-PC) trimer disks oriented in poly(vinyl alcohol) films (PVA) at room temperature and at 95 K were determined. Utilizing the known atomic coordinates of the chromophores (Schirmer, T., Bode, W. and Huber, R. (1987) J. Mol. Biol. 196, 677-695) and theoretical estimates of the orientations of the transition dipole moments relative to the molecular framework, the LD spectra were simulated using the pairwise exciton interaction model of Sauer and Scheer (Biochim. Biophys. Acta 936 (1988) 157-170); in this model, the alpha 84 and beta 84 transition moments are coupled by an exciton mechanism, while the beta 155 chromophore remains uncoupled. Linear dichroism spectra calculated using this exciton model, as well as an uncoupled chromophore (molecular) model, were compared with experimental LD spectra. Satisfactory qualitative agreement can be obtained in both the exciton and molecular models using somewhat different relative values of the theoretically estimated magnitudes of the beta 155 oscillator strength. Because the relative contributions of each of the chromophores (and thus exciton components) to the overall absorption of the C-PC trimer are not known exactly, it is difficult to differentiate successfully between the molecular and exciton models at this time. The linear dichroism spectra of PC dodecamers derived from phycobilisomes of Nostoc sp. oriented in stretched PVA films closely resemble those of the C-PC trimers from Mastigocladus laminosus, suggesting that the phycocyanin chromophores are oriented in a similar manner in both cases, and that neither linker polypeptides nor the state of aggregation have a significant influence on these orientations and linear dichroism spectra. The LD spectra of oriented phycocyanins in stretched PVA films at low temperatures (95 K) appear to be of similar quality and magnitude as the LD spectra of single C-PC crystals (Schirmer, T. and Vincent, M.G. (1987) Biochim. Biophys. Acta 893, 379-385).

Color↗
PubMed1991

Probing the primary quinone environment in photosynthetic bacterial reaction centers by light-induced FTIR difference spectroscopy.

The photoreduction of the primary electron acceptor, QA, has been characterized by light-induced Fourier transform infrared difference spectroscopy for Rb. sphaeroides reaction centers and for Rsp. rubrum and Rp. viridis chromatophores. The samples were treated both with redox compounds, which rapidly reduce the photooxidized primary electron P+, and with inhibitors of electron transfer from QA- to the secondary quinone QB. This approach yields spectra free from P and P+ contributions which makes possible the study of the microenvironment of QA and QA-.

Fourier Analysis↗