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Charlebois, Denis; Mauzerall, D.

doi:10.1023/a:1006199618668

Cited by 16 publications

(7 citation statements)

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“…Similar values of the thermal efficiency were found in the isolated PS I and PS II complexes in vitro ( , ). Note that the thermal efficiency of PS I on the millisecond time scale is ∼40% ( , ). The enthalpies for the formation of states P 700 + F AB - from P 700 * and Y Z • P 680 Q A - from P 680 * in vivo were estimated to be about −0.3 and −1 eV, respectively.…”

Section: Discussionmentioning

confidence: 99%

“…This conversion involves a variety of electron-transfer reactions on different time scales. Thermodynamic properties of these steps can be investigated by pulsed, time-resolved photoacoustic spectroscopy (), which was applied both to the primary processes of photosynthesis in the microsecond time window ( − ) and to the terminal charge stabilization on a time scale of milliseconds ( , ).…”

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confidence: 99%

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Thermodynamics of Electron Transfer in Oxygenic Photosynthetic Reaction Centers: Volume Change, Enthalpy, and Entropy of Electron-Transfer Reactions in the Intact Cells of the CyanobacteriumSynechocystisPCC 6803

2001

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The volume and enthalpy changes for charge transfer in the 0.1-10 micros time window in photosynthetic reaction centers of the intact cells of Synechocystis PCC 6803 were determined using pulsed, time-resolved photoacoustics. This required invention of a method to correct for the cell artifact at the temperature of maximum density of water caused by the heterogeneous system. Cells grown under either white or red light had different PS I/PS II molar ratios, approximately 3 and approximately 1.7, respectively, but invariable action spectra and effective antenna sizes of the photosystems. In both cultures, the photoacoustic measurements revealed that their thermodynamic parameters differed strongly in the spectral regions of predominant excitation of PS I (680 nm) and PS II (625 nm). On correcting for contribution of the two photosystems at these wavelengths, the volume change was determined to be -27 +/- 3 and -2 +/- 3 A3 for PS I and PS II, respectively. The energy storage on the approximately 1 micros time scale was estimated to be 80 +/- 15% and 45 +/- 10% per trap in PS I and PS II, respectively. These correspond to enthalpies of -0.33 +/- 0.2 and -1 +/- 0.2 eV for the assumed formation of ion radical pairs P700+F(AB-) and Y(Z*)P680Q(A-), respectively. Taking the free energy of the above reactions as the differences of their redox potentials in situ, apparent entropy changes were estimated to be +0.4 +/- 0.2 and -0.2 +/- 0.2 eV for PS I and PS II, respectively. These values are similar to that obtained in vitro for the purified reaction center complexes on the microsecond time scale [Hou et al. (2001) Biochemistry 40, 7109-7116, 7117-7125]. The constancy of these thermodynamic values over a 2-fold change of the ratio of PS I/PS II is support for this method of in vivo analysis. Our pulsed PA method can correct the "cell" or heterogeneous artifact and thus opens a new route for studying the thermodynamics of electron transfer in vivo.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Thermodynamics of Electron Transfer in Oxygenic Photosynthetic Reaction Centers: Volume Change, Enthalpy, and Entropy of Electron-Transfer Reactions in the Intact Cells of the CyanobacteriumSynechocystisPCC 6803

2001

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“…It should be noted that the photoacoustically measured ES efficiency within a certain time scale is an important parameter in defining the electron transport steps under observation. For example, about 40% of electrons are transferred from the RC to photoacoustically silent acceptors in PSII on the millisecond time scale (Cha and Mauzerall 1992;Charlebois and Mauzerall 1999). Nonetheless, it is clear that the inherently low ES efficiency in PSII is a consequence of a shallow excitonic trap, which although capable of oxidizing water, was appropriated from bacterial photosynthetic RCs and is not capable of reducing NADPH without a second photosystem.…”

Section: Discussionmentioning

confidence: 99%

“…The pulse intensity (in units of hits per RC) was estimated by titrating the PA signals versus the pulse energy and approximating the resulting profile with a one-hit Poisson distribution, as described by Charlebois and Mauzerall (1999). While measuring PA signals for open RCs, we applied the measuring pulses following at low repetition rate (\5 Hz).…”

Section: Methodsmentioning

confidence: 99%

Photosynthetic energy storage efficiency in Chlamydomonas reinhardtii, based on microsecond photoacoustics

et al. 2011

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Using a novel, pulsed micro-second time-resolved photoacoustic (PA) instrument, we measured thermal dissipation and energy storage (ES) in the intact cells of wild type (WT) Chlamydomonas reinhardtii, and mutants lacking either PSI or PSII reaction centers (RCs). On this time scale, the kinetic contributions of the thermal expansion component due to heat dissipation of absorbed energy and the negative volume change due to electrostriction induced by charge separation in each of the photosystems could be readily distinguished. Kinetic analysis revealed that PSI and PSII RCs exhibit strikingly different PA signals where PSI is characterized by a strong electrostriction signal and a weak thermal expansion component while PSII has a small electrostriction component and large thermal expansion. The calculated ES efficiencies at ~10 μs were estimated to be 80 ± 5 and 50 ± 13% for PSII-deficient mutants and PSI-deficient mutants, respectively, and 67 ± 2% for WT. The overall ES efficiency was positively correlated with the ratio of PSI to PSI + PSII. Our results suggest that the shallow excitonic trap in PSII limits the efficiency of ES as a result of an evolutionary frozen metabolic framework of two photosystems in all oxygenic photoautotrophs.

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“…18(2) de la Charte est différent de celui qui prévalait à l'époque de la Confédération lors de l'adoption de l'art. 133 104 . Comme mentionné plus haut, le magistrat ne s'est pas prononcé sur la question de savoir si les mécanismes d'interprétation ou de traduction simultanée étaient suffisants ou non : bien au contraire, il était d'avis que cette question n'était pas soulevée dans cette affaire 105 .…”

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Roy²

2016

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Le présent article vise à explorer la question de l’existence d’un droit constitutionnel du justiciable d’être compris dans l’une ou l’autre des langues officielles par les juges de la Cour suprême du Canada, sans l’entremise de services d’interprétation ou de traduction. La question ayant déjà reçu une réponse négative de la part de la Cour suprême du Canada en 1986 en ce qui concerne les tribunaux néo-brunswickois dans l’affaire Société des Acadiens c Association of Parents, le présent article tente plus précisément de trouver les bases sur lesquelles les tribunaux pourraient s’appuyer s’ils devaient rejeter ce précédent établi par la Cour suprême du Canada et reconnaître, devant cette Cour spécifiquement, le droit d’être compris directement dans l’une ou l’autre des langues officielles, sans services d’interprétation ou de traduction.

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Untitled

Cited by 16 publications

References 61 publications

Thermodynamics of Electron Transfer in Oxygenic Photosynthetic Reaction Centers: Volume Change, Enthalpy, and Entropy of Electron-Transfer Reactions in the Intact Cells of the CyanobacteriumSynechocystisPCC 6803

Thermodynamics of Electron Transfer in Oxygenic Photosynthetic Reaction Centers: Volume Change, Enthalpy, and Entropy of Electron-Transfer Reactions in the Intact Cells of the CyanobacteriumSynechocystisPCC 6803

Photosynthetic energy storage efficiency in Chlamydomonas reinhardtii, based on microsecond photoacoustics

De la possibilité d’être compris directement par les tribunaux canadiens, à l’oral comme à l’écrit, sans l’entremise de services d’interprétation ou de traduction

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