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Biomedical subjects

J Breton

Publications and source records attributed to J Breton.

At least 127 records · Page 7Linked to original sources
PubMed1986

Femtosecond spectroscopy of electron transfer in the reaction center of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26: Direct electron transfer from the dimeric bacteriochlorophyll primary donor to the bacteriopheophytin acceptor with a time constant of 2.8 +/- 0.2 psec.

The primary light-induced charge separation in reaction centers from Rhodopseudomonas sphaeroides R-26 has been investigated after excitation with laser pulses of 150 fsec duration within the longwave absorption band of the primary donor at 850 nm. An excited state of the primary donor, characterized by a broad absorption spectrum extending over the whole spectral range investigated (545-1240 nm), appeared within 100 fsec and gave rise to stimulated emission in the 870- to 1000-nm region with a 2.8-psec lifetime. The photooxidation of the primary donor, as measured at 1240 nm, and the photoreduction of the bacteriopheophytin acceptor, monitored at 545 nm and 675 nm, have been found to proceed simultaneously with a time constant of 2.8 +/- 0.2 psec. Kinetics of absorbance changes at other probe wavelengths gave no indication that an accessory bacteriochlorophyll is involved as a transient electron acceptor.

Journal Article↗
PubMed1986

Excitation trapping and primary charge stabilization in Rhodopseudomonas viridis cells, measured electrically with picosecond resolution.

The transmembrane primary charge separation in the photosynthetic bacterium Rhodopseudomonas viridis was monitored by electric measurements of the light-gradient type [Trissl, H. W. & Kunze, U. (1985) Biochim. Biophys. Acta 806, 136-144]. Excitation of whole cells with 30-ps laser pulses at either 532 nm or 1064 nm gave rise to a biphasic increase of the photovoltage. The fast phase, contributing about 50% of the total, rose with an exponential time constant </=40 ps and was independent of the redox state of the quinone electron acceptor. It is assigned to the migration of the excitation energy in the antenna and its subsequent trapping by the reaction center, monitored by the ultrafast charge separation between the primary electron donor and the bacteriopheophytin intermediary acceptor. The slower phase (125 +/- 50 ps) only occurred when the quinone was oxidized and disappeared when it was reduced (either chemically or photochemically). It is assigned to the forward electron transfer from the bacteriopheophytin to the quinone. The relative amplitudes of these two electrogenic steps demonstrate that the bacteriopheophytin intermediary acceptor is located halfway between the primary donor and the quinone.

Journal Article↗
PubMed1986

Streptococcus suis in slaughter pigs and abattoir workers.

The detection and identification of Streptococcus suis type 2 in 8.1% of 347 pig herds of southwestern Ontario revealed that the infection is widespread in this area. A herd suspected to be infected showed a carrier rate of 9.7% among the 62 animals sampled. These subclinical carriers represent a potential source of infection for slaughterhouse workers. From studies of contamination of hands and knives, it was concluded that eviscerators involved in removing the larynx and lungs from the carcasses have a significantly higher (p less than or equal to 0.05) risk of exposure to Streptococcus suis than other abattoir workers.

Abattoirs↗
PubMed1986

Isolation of Streptococcus suis using a selective medium.

A selective medium containing tryptic soy agar, 5% defibrinated bovine blood, crystal violet, nalidixic acid and gentamicin significantly improved the isolation rate of Streptococcus suis from tonsilar tissue of slaughtered pigs. Ninety-five percent of the S. suis isolates identified in Guelph were confirmed as S. suis in Copenhagen, but only six out of 21 isolates typed as capsular serotype 2 in Guelph were confirmed to possess serotype 2 antigen in Copenhagen. Sixty-four percent of the S. suis isolates were not typable within the current scheme of capsular serotypes from 1 to 13 and type 1/2.

Animals↗
PubMed1985

Experimental evidence for multistability in a photobiochemical system.

The kinetic behavior of a typical Hill reaction catalyzed by thylakoids and using the oxidized form of 2,6-dichloroindophenol (DCPIPox) as the artificial electron acceptor, is considered. Here, the light absorption process and the reduction of DCPIPox are autocatalytically coupled, leading to the occurrence of multiple steady states with respect to either the acceptor concentration or the incident light intensity. Experimental evidence is presented for both cases and the emergence of autocatalysis is discussed. The effect of the spatial arrangement on the global behavior of the system described is emphasized.

2,6-Dichloroindophenol↗
PubMed1984

HPLC purification of a biologically active membrane protein: the reaction center from photosynthetic bacteria.

Reaction centers from Rhodopseudomonas sphaeroides R 26 have been isolated from a crude extract obtained by lauryldimethylamine oxide extraction of chromatophore membranes, by HPLC using a combination of surface-mediated and size exclusion chromatography. The eluted RCs exhibit a normal activity (t 1/2 of the back-reaction is 70 ms) and are recovered in good yield (over 50% based on the activity) and purity (based on the A 280 nm/A 800 nm = 1.30 +/- 0.05 ratio and the characteristic 3 polypeptides SDS-PAGE pattern). The elution time (5-10 mn) is about two orders of magnitude faster than for the classical purification techniques.

Bacterial Proteins↗
PubMed1983

A master equation theory of fluorescence induction, photochemical yield, and singlet-triplet exciton quenching in photosynthetic systems.

A master equation theory is formulated to describe the dependence of the fluorescence yield (phi) in photosynthetic systems on the number of photons (Y) absorbed per photosynthetic unit (or domain). This theory is applied to the calculation of the dependence of the fluorescence yield on Y in (a) fluorescence induction, and (b) singlet exciton-triplet excited-state quenching experiments. In both cases, the fluorescence yield depends on the number of previously absorbed photons per domain, and thus evolves in a nonlinear manner with increasing Y. In case a, excitons transform the photosynthetic reaction centers from a quenching state to a nonquenching state, or a lower efficiency of quenching state; subsequently, absorbed photons have a higher probability of decaying by radiative pathways and phi increases as Y increases. In case b, ground-state carotenoid molecules are converted to long-lived triplet excited-state quenchers, and phi decreases as Y increases. It is shown that both types of processes are formally described by the same theoretical equations that relate phi to Y. The calculated phi (Y) curves depend on two parameters m and R, where m is the number of reaction centers (or ground-state carotenoid molecules that can be converted to triplets), and R is the ratio phi (Y leads to infinity)/(Y leads to 0). The finiteness of the photosynthetic units is thus taken into account. The m = 1 case corresponds to the "puddle" model, and m leads to infinity to the "lake," or matrix, model. It is shown that the experimental phi (Y) curves for both fluorescence induction and singlet-triplet exciton quenching experiments are better described by the m leads to infinity cases than the m = 1 case.

Kinetics↗
PubMed1983

[Effect of captopril in left ventricular failure during the acute stage of myocardial infarction].

The oral inhibitor of the converting enzyme of angiotensin has previously been used successfully in the treatment of chronic cardiac failure. Its action as an arterial and venous vasodilator and in significantly reducing the heart rate which we have previously reported, led us to assess its effects in left ventricular failure during acute myocardial infarction. The effects of captopril were compared with those of isosorbide dinitrate in 10 patients with left ventricular failure during acute myocardial infarction. An arterial and venous vasodilatation was obtained with both drugs. Captopril induced a greater fall in left ventricular filling pressures and significantly reduced the heart rate, leading to a slight increase in left ventricular systolic work index. Pulmonary arterial resistances decreased more significantly with captopril whilst systemic arterial resistances fell equally. The left ventricular function curve was shifted to the left by both captopril and isosorbide dinitrate, but only captopril induced an upward shift and only captopril caused very significant reductions in the rate-pressure product. The plasma renin activity of these patients was high but the correlation with the vasodilator effect was poor. There was little change in medium-term survival (50% mortality). These results indicate that captopril may be a valuable drug in the treatment of left ventricular failure in acute myocardial infarction. However, its oral presentation makes it difficult to determine the optimal dose.

Aged↗
PubMed1982

Orientation of gramicidin A transmembrane channel. Infrared dichroism study of gramicidin in vesicles.

Polarized infrared spectroscopy has been used to investigate the orientation of gramicidin A incorporated in dimyristoylphosphatidylcholine liposomes. Dichroism measurements of the major lipid (C = O ester, PO2-, CH2) and peptide (amide A, I, II) bands were performed on liposomes (with or without gramicidin) oriented by air-drying. The mean orientation of the lipid groups and of the pi LD helix chain in the gramicidin has been determined. It can be inferred from infrared frequencies of gramicidin that the dominant conformation of the peptide in liposomes cannot be identified to the antiparallel double-helical dimer found in organic solution. No shift in lipid frequencies was observed upon incorporation of gramicidin in the liposomes. However, a slight reorganization of the lipid hydrocarbon chains which become oriented more closely to the normal to the bilayer is evidenced by a change in the dichroism of the CH2 vibrations. The infrared dichroism results of gramicidin imply a perpendicular orientation of the gramicidin transmembrane channel with the pi LD helix axis at less than 15 degrees with respect to the normal to the bilayer.

Circular Dichroism↗
PubMed1981

Orientation of intrinsic proteins in photosynthetic membranes. Polarized infrared spectroscopy of chloroplasts and chromatophores.

In order to estimate the degree of orientation of the alpha-helices of intrinsic proteins in photosynthetic membranes, polarized infrared spectroscopy has been used to measure the dichroism of the amide I and amide II absorption bands of air-dried oriented samples of purple membranes, chloroplasts and chromatophores from Rhodopseudomonas sphaeroides. Using purple membrane, in which the orientation of the alpha-helices is precisely known (Henderson, R. (1977) Annu. Rev. Biophys. Bioeng. 6, 87-109), as a standard to calibrate our measurements and estimating the mosaic spread (extent of orientation) of the membranes from linear dichroism measurements performed in the visible spectral range, it is concluded that in photosynthetic membranes, the alpha-helices of intrinsic proteins are tilted at less than 40 degrees with respect to the normal to the plane of the membrane.

Amides↗
PubMed1981

[Incidence of infectious diseases in general practice. Results of a survey conducted in 1979 (author's transl)].

In 1979, a sample survey was conducted among 53 general practitioners to determine the incidence of infectious diseases in general medical practice. The survey showed that 45% of the patients seen by these doctors were suffering from an infection, that 53% of these (i.e. 24% of all patients) were treated with antibiotics and that G.P.'s play an important role in preventive medicine. These results might exert a useful influence on the teaching of infectious diseases to medical students and physicians.

Family Practice↗
PubMed1980

Orientation of the hemes of high potential cytochromes relative to photosynthetic membranes, as shown by the linear dichroism of oriented preparations.

The orientations of high potential cytochromes with respect to photosynthetic membranes was investigated in spinach chloroplasts and in Rhodopseudomonas viridis. The general approach consists in detection with polarized light of photoinduced absorbance changes related to the oxidation of the cytochromes. The orientation of cytochrome c-558 was measured at room temperature in chromatophores and whole cells of Rps. viridis, oriented on glass slides and in a magnetic field, respectively. The orientation of cytochrome b-559 of green plants was detected at 77 K in magnetically oriented chloroplasts. In both cases the dichroic ratio for the alpha band shows that the heme plane makes an angle greater than 35 degrees C with the membrane plane. Moreover, the dichroic ratio is not constant throughout the alpha and beta bands, for both cytochrome c-558 and b-559. Linear dichroism spectra of oriented pure horse heart cytochrome c and cytochrome c2 of Rhodopseudomonas sphaeroides in stretched polyvinyl alcohol films show that the variations of the dichroic ratio in the alpha and beta bands can be explained by the occurrence of x- and y-polarized transitions absorbing at slightly different wavelengths.

Chloroplasts↗
PubMed1979

Quenching of fluorescence by triplet excited states in chloroplasts.

The fluorescence quantum yield in spinach chloroplasts at room temperature has been studied utilizing a 0.5-4.0 mus duration dye laser flash of varying intensities as an excitation source. The yield (phi) and carotenoid triplet concentration were monitored both during and following the laser flash. The triplet concentration was monitored by transient absorption spectoscopy at 515 nm, while the yield phi following the laser was probed with a low intensity xenon flash. The fluorescence is quenched by factors of up to 10-12, depending on the intensity of the flash and the time interval following the onset of the flash. This quenching is attributed to a quencher Q whose concentration is denoted by Q. The relative instantaneous concentration of Q was calculated from phi utilizing the Stern-Volmer equation, and its buildup and decay kinetics were compared to those of carotenoid triplets. At high flash intensities (greater than 10(16) photon . cm-2) the decay kinetics of Q are slower than those of the carotenoid triplets, while at lower flash intensities they are similar. Q is sensitive to oxygen and it is proposed that Q, at the higher intensities, is a trapped chlorophyll triplet. This hypothesis accounts well for the continuing rise of the carotenoid triplet concentration for 1-2 mus after the cessation of the laser pulse by a slow detrapping mechanism, and the subsequent capture of the triplet energy by carotenoid molecules. At the maximum laser intensities, the carotenoid triplet concentration is about one per 100 chlorophyll molecules. The maximum chlorophyll ion concentration generated by the laser pulses was estimated to be below 0.8 ions/100 chlorophyll molecules. None of the observations described here were altered when a picosecond pulse laser train was substituted for the microsecond pulse. A simple kinetic model describing the generation of singlets and triplets (by intersystem crossing), and their subsequent interaction leading to fluorescence quenching, accounts well for the observations. The two coupled differential equations describing the time dependent evolution of singlet and triplet excited states are solved numerically. Using a single-triplet bimolecular rate constant of gammast = 10(-8) cm3 . s-1, the following observations can be accounted for: (1) the rapid initial drop in phi and its subsequent levelling off with increasing time during the laser pulse, (2) the buildup of the triplets during the pulse, and (3) the integrated yield of triplets per pulse as a function of the energy of the flash.

Carotenoids↗