Search PubMed⌕ Search

Biomedical subjects

J Breton

Publications and source records attributed to J Breton.

At least 109 records · Page 6Linked to original sources
PubMed1990

Characterization by FTIR spectroscopy of the photoreduction of the primary quinone acceptor QA in photosystem II.

Molecular changes associated with the photoreduction of the primary quinone acceptor Qa of photosystem II have been characterized by Fourier transform infrared spectroscopy. This reaction was light-induced at room temperature on photosystem II membranes in the presence of hydroxylamine and diuron. A positive signal at 1478 cm-1 is assigned to the C---O stretching mode of the semiquinone anion, and can be correlated to the negative C=O mode(s) of the neutral QA at 1645 cm-1 and/or 16 cm-1. Analogies with bacterial reaction center are found in the amide I absorption range at 1672 cm-1, 1653 cm-1 and 1630 cm-1. The stabilization of QA- does not result from a large protein conformation change, but involves perturbations of several amino acid vibrations. At 1658 cm-1, a negative feature sensitive to 1H-2H exchange is tentatively assigned to a NH2 histidine mode, while tryptophan D2252 could contribute to the signal at 1560/1550 cm-1.

Amino Acids↗
PubMed1990

A protein conformational change associated with the photoreduction of the primary and secondary quinones in the bacterial reaction center.

A comparison is made between the PQA----P+QA- and PQAQB----P+QAQB-transitions in Rps. viridis and Rb. sphaeroides reaction centers (RCs) by the use of light-induced Fourier transform infrared (FTIR) difference spectroscopy. In Rb. sphaeroides RCs, we identify a signal at 1650 cm-1 which is present in the P+QA-minus-PQA spectrum and not in the P+QAQB(-)-minus-PQAQB spectrum. In contrast, this signal is present in both P+QA(-)-minus-PQA- and P+QAQB(-)-minus-PQAQB spectra of Rps. viridis RCs. These data are interpreted in terms of a conformational change of the protein backbone near QA (possible at the peptide C = O of a conserved alanine residue in the QA pocket) and of the different bonding interactions of QB with the protein in the RC of the two species.

Bacterial Proteins↗
PubMed1990

Partial symmetrization of the photosynthetic reaction center.

The bacterial photosynthetic reaction center (RC) is a pigmented intrinsic membrane protein that performs the primary charge separation event of photosynthesis, thereby converting light to chemical energy. The RC pigments are bound primarily by two homologous peptides, the L and M subunits, each containing five transmembrane helices. These alpha helices and pigments are arranged in an approximate C2 symmetry and form two possible electron transfer pathways. Only one of these pathways is actually used. In an attempt to identify nonhomologous residues that are responsible for functional differences between the two branches, homologous helical regions that interact extensively with the pigments were genetically symmetrized (that is, exchanged). For example, replacement of the fourth transmembrane helix (D helix) in the M subunit with the homologous helix from the L subunit yields photosynthetically inactive RCs lacking a critical photoactive pigment. Photosynthetic revertants have been isolated in which single amino acid substitutions (intragenic suppressors) compensate for this partial symmetrization.

Amino Acid Sequence↗
PubMed1990

Fourier transform infrared difference spectroscopy shows no evidence for an enolization of chlorophyll a upon cation formation either in vitro or during P700 photooxidation.

Molecular changes associated with the photooxidation of the primary electron donor P700 in photosystem I from cyanobacteria have been investigated with Fourier transform infrared (FTIR) difference spectroscopy. Highly resolved signals are observed in the carbonyl stretching frequency region of the light-induced FTIR spectra. In order to assign and to interpret these signals, the FTIR spectra of isolated chlorophyll a and pyrochlorophyll a (lacking the 10a-ester carbonyl) in both their neutral and cation states were investigated. Comparison of the redox-induced FTIR difference spectra of these two model compounds demonstrates that upon chlorophyll a cation formation in tetrahydrofuran the 7c-ester carbonyl is essentially unperturbed while the 10a-ester carbonyl is upshifted from 1738 to 1751 cm-1. For the 9-keto group, the shift is from 1693 to 1718 cm-1 in chlorophyll a and from 1686 to 1712 cm-1 in pyrochlorophyll a. The 1718-cm-1 band in the difference spectrum of chlorophyll a is thus unambiguously assigned to the 9-keto carbonyl of the cation. Comparison of the light-induced FTIR difference spectrum associated with the photooxidation of P700 in vivo with the difference FTIR spectrum of chlorophyll a cation formation leads to the assignment of the frequencies of the 9-keto carbonyl group(s) at 1700 cm-1 in P700 and at 1717 cm-1 in P700+.(ABSTRACT TRUNCATED AT 250 WORDS)

Cations↗
PubMed1990

Redox-linked conformational changes in proteins detected by a combination of infrared spectroscopy and protein electrochemistry. Evaluation of the technique with cytochrome c.

We have developed a new technique for the study of redox-linked conformational changes in proteins, by the combination of two established techniques. Fourier-transform infrared spectroscopy has been used together with direct electrochemistry of the protein at a modified metal electrode surface. The technique has been evaluated with cytochrome c, because of its well-characterized electrochemistry and because the availability of X-ray crystallographic and NMR studies of both redox states of the protein provides a reference against which our data can be compared. In electrochemical control experiments, it was confirmed that the spectroelectrochemical cell design allows fast, accurate and reproducible control of the redox poise of the protein. The resulting reduced-minus-oxidized infrared difference spectra show the changes in the frequencies and intensities of molecular vibrations which arise from the redox-linked conformational change. In contrast to the absolute infrared spectra of proteins, such difference spectra can be sufficiently straightforward to allow interpretation at the level of individual bonds. A complete interpretation of the spectra is beyond the scope of the present paper: however, on the basis of the data presented, we are able to suggest assignments for all except one of the major bands between 1500 cm-1 and 1800 cm-1.

Animals↗
PubMed1990

Interleukin-1 release by rat synovial cells is dependent on sequential treatment with gamma-interferon and lipopolysaccharide.

To determine the potential regulatory mechanisms involved in synovial cell interleukin-1 (IL-1) release, the ability of gamma-interferon (gamma-IFN) to influence IL-1 release was assessed. Rat synovial cells cultured in the presence of a variety of stimuli, including lipopolysaccharide (LPS), failed to release IL-1. However, pretreatment of synovial cells with gamma-IFN, followed by LPS stimulation, resulted in increased levels of intracellular IL-1 as well as release of IL-1 from the cell. The level of IL-1 release was dependent on the concentration of both gamma-IFN and LPS, and on length of exposure to the gamma-IFN. The kinetic and dose requirements for gamma-IFN-dependent IL-1 release were similar to those for Ia antigen expression, but LPS was necessary for IL-1 messenger RNA induction, intracellular IL-1 accumulation, and IL-1 release. In addition, sequential treatment, i.e., gamma-IFN followed by LPS, was essential for IL-1 induction. Substitution of phorbol ester or calcium ionophore for gamma-IFN did not result in similar IL-1 release. In addition, induction of IL-1 messenger RNA by another stimulus was not sufficient to result in IL-1 release following LPS treatment. These results suggest that release of IL-1 by rat synovial cells requires the production of a regulatory signal, which is inducible by gamma-IFN.

Animals↗
PubMed1990

Initial characterization of site-directed mutants of tyrosine M210 in the reaction centre of Rhodobacter sphaeroides.

A description of the properties of site-directed mutants of the reaction centre (RC) of Rhodobacter sphaeroides is presented. The residue tyrosine M210 (YM210) has been changed to phenylalanine (FM210) and leucine (LM210). Both mutants grew photoheterotrophically under conditions of high light but only the FM210 mutant grew under low light. Photobleaching spectra of chromatophores isolated from these mutants showed that the amount of functional RC was comparable to wild-type and that the spectral features were essentially unchanged. Shifts were observed in the absorption spectra in regions attributable to all the chromophores. An increase in intensity and a 3 nm red shift (from 803 to 806 nm) was observed in the Qy band of the monomer bacteriochlorophylls. A new extinction coefficient for the RC was determined at 806 nm (332 +/- 15 mM-1 cm-1). Linear dichroism (LD) spectra showed that there was no significant large scale change in the angles of the individual pigments relative to the C2 axis of symmetry. Cytochrome turnover assays were performed on isolated RC and light harvesting I complex (LH I)-RC (photosynthetic units, PSU) preparations. A turnover number of 120 cyt RC-1 s-1 was calculated for both the mutants while wild-type had a turnover number of 228 cyt RC-1 s-1. The cytochrome c2-mediated re-reduction kinetics of P+ were comparable to those observed in the wild-type. The half-time of charge recombination within the RC increased in the mutants to the wild-type (100 ms in the wild type, and 150 and 200 ms in FM210 and LM210, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Proteins↗
PubMed1990

Content and methods of studies on the prevention and treatment of mental disorders in selected psychiatric journals.

Studies on psychiatric treatments published in 1986 were reviewed in five major psychiatric journals (Am. J. Psychiatry, Can. J. Psychiatry, Arch. Gen. Psychiatry, Am. J. Orthopsychiatry and Am. Acad. Child Psychiatry). Articles on prevention and treatment represent only 27% of the total of titles (194 out of 731 articles). The studies reviewed focus mostly on the treatment of adults, on psychoses, on the short term effect of treatment and on the effect of treatment rather than its process. Almost no information is published on the evaluation of the process or on the cost of treatment. Studies are for the most part original, but they tend to be studies without controls rather than randomized or non-randomized controlled trials. Interpretation of results rely essentially on statistical significance and almost no attention is paid to the evaluation of impact, in epidemiological terms, of the cause-effect relationship and to the clinical relevance of observed differences. Psychiatrists who read only a few major journals of psychiatry should get more information on therapeutic and preventive interventions in comparison to other components of clinical work and to clinical course of disease.

Humans↗
PubMed1988

The orientation of beta-sheets in porin. A polarized Fourier transform infrared spectroscopic investigation.

The orientation of the protein secondary structures in porin is investigated by Fourier transform infrared (FTIR) linear dichroism of oriented multilayers of porin reconstituted in lipid vesicles. The FTIR absorbance spectrum shows the amide I band at 1,631 cm-1 and several shoulders around 1,675 cm-1 and at 1,696 cm-1 indicative of antiparallel beta-sheets. The amide II is centered around 1,530 cm-1. The main dichroic signals peak at 1,738, 1,698, 1,660, 1,634, and 1,531 cm-1. The small magnitude of the 1,634 cm-1 and 1,531 cm-1 positive dichroism bands demonstrates that the transition moments of the amide I and amide II vibrations are on the average tilted at 47 degrees +/- 3 degrees from the membrane normal. This indicates that the plane of the beta-sheets is approximately perpendicular to the bilayer. From these IR dichroism results and previously reported diffuse x-ray data which revealed that a substantial number of beta-strands are nearly perpendicular to the membrane, a model for the packing of beta-strands in porin is proposed which satisfies both IR and x-ray requirements. In this model, the porin monomer consists of at least two beta-sheet domains, both with their plane perpendicular to the membrane. One sheet has its strands direction lying nearly parallel to the membrane normal while the other sheet has its strands inclined at a small angle away from the membrane plane.

Bacterial Outer Membrane Proteins↗
PubMed1988

Infrared spectroelectrochemistry of bacteriochlorophylls and bacteriopheophytins: Implications for the binding of the pigments in the reaction center from photosynthetic bacteria.

The IR spectra of the bacteriochlorophyll a and b cations and the bacteriopheophytin a and b anions were obtained by using an IR and optically transparent electrochemical cell. Prominent effects of radical formation on the vibrational spectra were found for bands assigned to the ester, keto, and acetyl C=O groups and for vibrations from macrocycle bonds. The (radical-minus-neutral) difference spectra are compared to the light-induced difference spectra of the primary donor photooxidation and the intermediary acceptor photoreduction in the reaction center of photosynthetic bacteria. Light-induced absorbance changes from bacteriochlorophyll a-containing reaction centers bear striking similarities to the electrochemically induced absorbance changes observed upon formation of bacteriochlorophyll a(+)in vitro. Comparison of the radical formation in vitro in a hydrogen-bonding or a nonhydrogen-bonding solvent suggests an ester C=O group hydrogen bonded in the neutral state but free in the cation state. For the keto C=O group, the same comparison indicates one free carbonyl group. The (anion-minus-neutral) difference spectra of bacteriopheophytin a and b exhibit a single band in the ester C=O frequency range. In contrast, two bands are observed in the difference spectra of the intermediary acceptor reduction in the reaction center of Rhodopseudomonas viridis. The higher frequency band exhibits a sensitivity to (1)H-(2)H exchange, which suggests a contribution from a protonated carboxyl group of an amino acid side chain.

Journal Article↗
PubMed1987

[Medical jurisprudence problems raised by transsexualism in 1986. Apropos of 148 cases of gender dysphoria].

The authors review the classification of transsexualism and gender dysphoria with respect to a series of 148 patients followed up for 10 years by a multidisciplinary group of endocrinologists, surgeons and psychiatrists; transsexualism is a major problem of self-identity and not a sexual derivation. The principal features of the study population are presented with details of methodology, criteria for selection for sex change treatment, and results obtained. The two main medicolegal problems (changing civil identity and penal medical responsibility) posed by medico-surgical treatment in France are discussed.

Diagnosis, Differential↗
PubMed1986

Femtosecond spectroscopy of excitation energy transfer and initial charge separation in the reaction center of the photosynthetic bacterium Rhodopseudomonas viridis.

Reaction centers from the photosynthetic bacterium Rhodopseudomonas viridis have been excited within the near-infrared absorption bands of the dimeric primary donor (P), of the "accessory" bacteriochlorophylls (B), and of the bacteriopheophytins (H) by using laser pulses of 150-fsec duration. The transfer of excitation energy between H, B, and P occurs in slightly less than 100 fsec and leads to the ultrafast formation of an excited state of P. This state is characterized by a broad absorption spectrum and exhibits stimulated emission. It decays in 2.8 +/- 0.2 psec with the simultaneous oxidation of the primary donor and reduction of the bacteriopheophytin acceptor, which have been monitored at 545, 675, 815, 830, and 1310 nm. Although a transient bleaching relaxing in 400 +/- 100 fsec is specifically observed upon excitation and observation in the 830-nm absorption band, we have found no indication that an accessory bacteriochlorophyll is involved as a resolvable intermediary acceptor in the primary electron transfer process.

Journal Article↗
PubMed1986

Dissipative structures in a two-cell system: Numerical and experimental approaches.

It has been shown that the coupling between the photoreduction of the oxidized form of dichloroindophenol (an artificial electron acceptor) by thylakoids and the incident light intensity can lead to the appearance of multiple steady states when the system is operated under open conditions. In the present work, a numerical study and experimental evidence are presented on the occurrence of dissipative structures in an arrangement of two continuously stirred tank reactors with mutual mass exchange of dichloroindophenol through an inert membrane. The stable spatial structures are generated by the creation of transient internal and external asymmetries. A nontrivial hysteresis effect between symmetric and asymmetric stable steady states has been observed.

Journal Article↗