Pierre Joliot - Academia.edu (original) (raw)

Papers by Pierre Joliot

Research paper thumbnail of Mechanism of electron transfer in the cytochrome b/f complex of algae: evidence for a semiquinone cy

The most widely accepted mechanism of electron and proton transfer within the cytochrome (Cyt) b/... more The most widely accepted mechanism of electron and proton transfer within the cytochrome (Cyt) b/f complex derives from the Q-cycle hypothesis originally proposed for the mitochondrial Cyt b/c1 complex by Mitchell [Mitchell, P. (1975) FEBS Lett. 57, 135-137]. In chloroplasts, the Cyt b/f complex catalyzes the oxidation of a plastoquinol at a site, Qo (the plastoquinol binding site), close to the inner aqueous phase and the reduction of a quinone at a site, Qi (the plastoquinone binding site), close to the stromal side of the membrane. In an alternative model, the semiquinone cycle [Wikström, M. & Krab, K. (1986) J. Bioenerg. Biomembr. 18, 181-193], a charged semiquinone formed at site Qo is transferred to site Qi where it is reduced into quinol. Flash-induced kinetics of the redox changes of Cyt b and of the formation of a transmembrane potential have been measured in Chlorella sorokiniana cells incubated in reducing conditions that induce a full reduction of the plastoquinone pool. The experiments were performed in the presence of an uncoupler that collapses the permanent electrochemical proton gradient and thus accelerates the rate of the electrogenic processes. The results show that the electrogenic reaction driven by the Cyt b/f complex precedes the processes of reduction or oxidation of the b-hemes. This electrogenic process is probably due to a transmembrane movement of a charged semiquinone, in agreement with the semiquinone-cycle hypothesis. This mechanism may represent an adaptation to reducing conditions when no oxidized quinone is available at the Qi site.

Research paper thumbnail of Period-four oscillations of the flash-induced oxygen formation in photosynthesis

Photosynthesis research, 2003

In this minireview, the earlier researches that led to the discovery of the period-four oscillati... more In this minireview, the earlier researches that led to the discovery of the period-four oscillations of the flash-induced oxygen formation are presented. It also includes the background of the classical model proposed by Bessel Kok, in which the formation of oxygen requires the sequential accumulation of four positive charges on the donor side of the same reaction center.

Research paper thumbnail of Mechanism of electron transfer in the cytochrome b/f complex of algae: evidence for a semiquinone cycle

Proceedings of the National Academy of Sciences of the United States of America, 1994

The most widely accepted mechanism of electron and proton transfer within the cytochrome (Cyt) b/... more The most widely accepted mechanism of electron and proton transfer within the cytochrome (Cyt) b/f complex derives from the Q-cycle hypothesis originally proposed for the mitochondrial Cyt b/c1 complex by Mitchell [Mitchell, P. (1975) FEBS Lett. 57, 135-137]. In chloroplasts, the Cyt b/f complex catalyzes the oxidation of a plastoquinol at a site, Qo (the plastoquinol binding site), close to the inner aqueous phase and the reduction of a quinone at a site, Qi (the plastoquinone binding site), close to the stromal side of the membrane. In an alternative model, the semiquinone cycle [Wikström, M. & Krab, K. (1986) J. Bioenerg. Biomembr. 18, 181-193], a charged semiquinone formed at site Qo is transferred to site Qi where it is reduced into quinol. Flash-induced kinetics of the redox changes of Cyt b and of the formation of a transmembrane potential have been measured in Chlorella sorokiniana cells incubated in reducing conditions that induce a full reduction of the plastoquinone pool....

Research paper thumbnail of Dissipation in bioenergetic electron transfer chains

Photosynthesis Research, 1996

This paper examines the processes by which wasteful dissipation of free energy may occur in bioen... more This paper examines the processes by which wasteful dissipation of free energy may occur in bioenergetic electron transfer chains. Frictionless transfer requires high rate constants in order to achieve a quasi-equilibrium steady-state. Previous results concerning the maximum power available from a photochemical source are recalled. The energetic performance of the bacterial reaction center is discussed, characterizing the processes that decrease either the quantum yield (recombination and obstruction) or the chemical potential (friction and non-equilibrated mechanisms). Considering the whole chain, diffusive carriers are potentially weaker links, due to kinetic limitation and short-circuiting reactions. It is suggested that the evolutionary trend has been to limit their number by lumping them into tightly bound protein complexes or, in a more flexible way, into labile supercomplexes.

Research paper thumbnail of Advances in photosynthesis and respiration : Including bioenergy and related processes: a new look beginning with volume 35

Photosynthesis research, 2012

This review provides a brief historical account of how microscopical studies of chloroplasts have... more This review provides a brief historical account of how microscopical studies of chloroplasts have contributed to our current knowledge of the structural and functional organization of thylakoid membranes. It starts by tracing the origins of the terms plastid, grana, stroma and chloroplasts to light microscopic studies of 19th century German botanists, and then describes how different types of electron microscopical techniques have added to this field. The most notable contributions of thin section electron microscopy include the elucidation of the 3-D organization of thylakoid membranes, the discovery of prolamellar bodies in etioplasts, and the structural changes in thylakoid architecture that accompany the light-dependent transformation of etioplasts into chloroplasts. Attention is then focused on the roles that freeze-fracture and freeze-etch electron microscopy and immuno electron microscopy have played in defining the extent to which the functional complexes of thylakoids are non-randomly distributed between appressed, grana and non-appressed stroma thylakoids. Studies reporting on how this lateral differentiation can be altered experimentally, and how the spatial organization of functional complexes is affected by alterations in the light environment of plants are also included in this discussion. Finally, the review points to the possible uses of electron microscope tomography techniques in future structural studies of thylakoid membranes.

Research paper thumbnail of Flash-induced oxidation of cytochrome b-563 in algae under anaerobic conditions: Effect of dinitrophenylether of iodonitrothymol

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1987

ABSTRACT

Research paper thumbnail of Supramolecular membrane protein assemblies in photosynthesis and respiration

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1993

Research paper thumbnail of The pH dependence of the redox midpoint potential of the 2Fe2S cluster from cytochrome b6f complex (the ‘Rieske centre’)

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1992

... 4()265 Rapid Report The pH dependence of the redox midpoint potential of the 2Fe2S cluster fr... more ... 4()265 Rapid Report The pH dependence of the redox midpoint potential of the 2Fe2S cluster from cytochrome b6f complex(the 'Rieske centre') Wolfgang Nitschke ~', Pierre Joliot ~', Ursula Liebl h A. William Rutherford h Giinter Hauska ~, Adolf Miiller J ... Healhcote+ P. and Moss. ...

Research paper thumbnail of Electron transfer between the two photosystems. I. Flash excitation under oxidizing conditions

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1984

ABSTRACT

Research paper thumbnail of Proton pumping and electron transfer in the cytochrome bf complex of algae

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1986

ABSTRACT

Research paper thumbnail of Excitation transfer between photosynthetic units: the 1964 experiment

Photosynthesis research, 2003

We review here the background and the experiments that led to the concept of excitation energy tr... more We review here the background and the experiments that led to the concept of excitation energy transfer among photosystem (PS) II units. On the basis of a kinetic analysis of oxygen evolution and chlorophyll a fluorescence yield, the authors showed, in 1964, that the PS II photochemical reaction involved in the formation of oxygen is not a first-order process. We concluded that excitation energy localized in a 'photosynthetic unit' including a reduced primary acceptor is transferred with a high probability to neighboring PS II units. Here, the beginnings and the original data of this topic are presented.

Research paper thumbnail of Supramolecular organization of the photosynthetic chain in chromatophores and cells of Rhodobacter sphaeroides

Photosynthesis Research, 1996

Flash-induced kinetics of the membrane potential increase related to electron transfer within the... more Flash-induced kinetics of the membrane potential increase related to electron transfer within the cytochrome (cyt) b/c1 complex (Phase III) and that of cyt c1+c2 reduction have been measured as a function of myxothiazol concentration in isolated chromatophores and whole cells of Rhodobacter sphaeroides. Upon addition of nonsaturating concentrations of myxothiazol, kinetics of Phase III display two phases, Phase IIIa and Phase IIIb. The amplitude of Phase IIIa, completed in about 10 ms, is proportional to the fraction of non-inhibited cyt b/c1 complexes, while its half-time is independent of the myxothiazol concentration. A fast cyt c1+c2 reduction phase is correlated to Phase IIIa. These experiments demonstrate that, in a range of time of several ms, diffusion of cyt c2 is restricted to domains formed by a supercomplex including two reaction centers (RCs) and a single cyt b/c1 complex, as proposed by Joliot et al. (Biochim Biophys Acta 975: 336-345, 1989). Phase IIIb, completed in about 100 ms, shows that positive charges or inhibitor molecules are exchanged between supercomplexes in this range of time. These exchanges occur within domains including 2 to 3 supercomplexes, i.e. in membrane domains smaller than a single chromatophore. These conclusions apply to both isolated chromatophores and whole cells.

Research paper thumbnail of COMPARAISON ENTRE L'EMISSION D'OXYGENE ET L'EMISSION DE LUMINESCENCE A LA SUITE D'UNE SERIE D'ECLAIRS SATURANTS

Photochemistry and Photobiology, 1970

ABSTRACT Abstract— Luminescence of Chlorella cells has been measured after illumination by a seri... more ABSTRACT Abstract— Luminescence of Chlorella cells has been measured after illumination by a series of short saturating flashes.The intensity of luminescence is strongly dependent upon the number of flashes; luminescence is minimum after a single flash and maximum after a double flash illumination.Ifl/n is the intensity of luminescence measured 0.24 sec after the nth flash, the series ln shows oscillations as a function of n. The series ln is very similar to the series yn, in which y is the amount of oxygen evolved by the nth flash, the term ln corresponding to the term yn+1. To interpret the oscillations of the series yn, different models of system II photochemical centers have been proposed, one by ourselves and the other one by KOK et al. In these models the electron donor Z of photosystem 11 is supposed to have 2 or 4 levels of oxidation, the more oxidized state being the precursor of oxygen. These different oxidation states of the donor Z allow storage of the photic energy in the system. The correlation between the series yn and ln shows that at least one of the oxidized forms of the donor Z is a substrate for the luminescence reaction.

Research paper thumbnail of Glu78, from the Conserved PEWY Sequence of Subunit IV, Has a Key Function in Cytochrome b 6 f Turnover †

Biochemistry, 1998

We have investigated the structure to function relationship at the Qo site in cytochrome b6f comp... more We have investigated the structure to function relationship at the Qo site in cytochrome b6f complexes in vivo. To this end, we created site-directed mutants of Chlamydomonas reinhardtii, at position 78 in the sequence of subunit IV. The target glutamic acid, present in the highly conserved 77PEWY80 sequence, was changed to residues of different polarities which did not prevent the functional assembly of cytochrome b6f complexes. Spectroscopic analysis performed in anaerobic conditions in vivo revealed distinct alterations in cytochrome b6f function, depending on the nature of the substituted residue. The semiconservative E78D substitution, in which only the length of the side chain is reduced, retained the functional features of the wild-type configuration. The E78K and E78L substitutions caused a significant decrease, by factors of 3 and 5, respectively, in the rate of the concerted oxidation process at the Qo site without a change in the affinity of Qo for reduced plastoquinones. The E78Q and E78N substitutions modified the characteristics of cytochrome b6f turnover under repetitive flash illumination. They caused a large increase in the electrogenicity of the electron-transfer reactions through the mutated cytochrome b6f complex. This increase was specifically sensitive to the electrical component of the proton-motive force. Surprisingly, despite the larger number of charges translocated across the membrane per charge injected in the high potential chain, the reduction phase for cytochrome b6 became barely detectable in the mutants, unless inhibitors at the Qi site were present. We show that similar functional characteristics can be observed with the cytochrome b6f complex in the wild-type in anaerobic conditions, provided a single flash illumination regime is used. These observations suggest that cytochrome b6f turnover may involve a mechanism implying an extra proton pumping activity.

Research paper thumbnail of On the advantages of using green light to study fluorescence yield changes in leaves

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2007

In photosynthetic chains, the kinetics of fluorescence yield depends on the photochemical rates a... more In photosynthetic chains, the kinetics of fluorescence yield depends on the photochemical rates at the level of both Photosystem I and II and thus on the absorption cross section of the photosynthetic units as well as on the coupling between light harvesting complexes and photosynthetic traps. A new set-up is described which, at variance with the commonly used set-ups, uses of a weakly absorbed light source (light-emitting diodes with maximum output at 520 nm) to excite the photosynthetic electron chain and probe the resulting fluorescence yield changes and their time course. This approach optimizes the homogeneity of the exciting light throughout the leaf and we show that this homogeneity narrows the distribution of the photochemical rates. Although the exciting light is weakly absorbed, the possibility to tune the intensity of the light emitting diodes allows one to reach photochemical rates ranging from 10 4 s − 1 to 0.25 s − 1 rendering experimentally accessible different functional regimes. The variations of the fluorescence yield induced by the photosynthetic activity are qualitatively and quantitatively discussed. When illuminating dark-adapted leaves by a weak light, the kinetics of fluorescence changes displays a pronounced plateau which precedes the fluorescence increase reflecting the full reduction of the plastoquinone pool. We ascribe this plateau to the time delay needed to reduce the photosystem I electron acceptors.

Research paper thumbnail of Equilibration between cytochrome f and P700 in intact leaves

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2005

Electron transport between the two photosynthetic reaction centres of high plants is mediated by ... more Electron transport between the two photosynthetic reaction centres of high plants is mediated by plastoquinone, a rieske iron-sulfur centre, cytochrome f and plastocyanin. Measurements of redox equilibration amongst these have produced confusing results, with apparent equilibrium constants being estimated that are inconsistent with in vitro measurements of redox midpoint potentials of the components concerned.

Research paper thumbnail of Fast oxidation of the primary electron acceptor under anaerobic conditions requires the organization of the photosynthetic chain of in supercomplexes

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2005

The kinetics of reoxidation of the primary acceptor Q a has been followed by measuring the change... more The kinetics of reoxidation of the primary acceptor Q a has been followed by measuring the changes in the fluorescence yield induced by a series of saturating flashes in intact cells of Rhodobacter sphaeroides in anaerobic conditions. At 0 8C, about half of Q a À is reoxidized in about 200 ms while reoxidation of the remaining fraction is completed in several seconds to minutes. The fast phase is associated with the transfer of ubiquinone formed at site Q o of the cytochrome bc 1 complex while the slowest phase is associated with the diffusion of ubiquinone present in the membrane prior to the flash excitation. The biphasic kinetics of Q a À oxidation is interpreted assuming that the electron chain is organized in supercomplexes that associate two RCs and one cyt bc 1 complex, which allows a fast transfer of quinone formed at the level of cyt bc 1 complex to the RCs. In agreement with this model, the fast phase of Q a À reoxidation is inhibited by myxothiazol, a specific inhibitor of cyt bc 1 . The PufX-deleted mutant displays only the slowest phase of Q a À oxidation; it is interpreted by the lack of supramolecular organization of the photosynthetic chain that leads to a larger average distance between cyt bc 1 and RCs. D

Research paper thumbnail of Slow electrogenic phase and intersystem electron transfer in algae

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1985

ABSTRACT

Research paper thumbnail of Flash-induced 519 nm absorption change in green algae

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1974

... Printed in The Netherlands BBA 46772 FLASHINDUCED 519 nm ABSORPTION CHANGE IN GREEN ALGAE PIE... more ... Printed in The Netherlands BBA 46772 FLASHINDUCED 519 nm ABSORPTION CHANGE IN GREEN ALGAE PIERRE JOLIOT and RENE DELOSME lnstitut de ... On the other hand, Nam HaiChua and Levine [6] observed that this mutant displays an abnormally large 520 nm ...

Research paper thumbnail of Cyclic electron flow in C3 plants

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2006

This paper summarized our present view on the mechanism of cyclic electron flow in C3 plants. We ... more This paper summarized our present view on the mechanism of cyclic electron flow in C3 plants. We propose that cyclic and linear pathways are in competition for the reoxidation of the soluble primary PSI acceptor, Ferredoxin (Fd), that freely diffuses in the stromal compartment. In the linear mode, Fd binds ferredoxin-NADP-reductase and electrons are transferred to NADP + and then to the Benson and Calvin cycle. In the cyclic mode, Fd binds a site localized on the stromal side of the cytochrome b 6 f complex and electrons are transferred to P 700 via a mechanism derived from the Q-cycle. In dark-adapted leaves, the cyclic flow operates at maximum rate, owing to the partial inactivation of the Benson and Calvin cycle. For increasing time of illumination, the activation of the Benson and Calvin cycle, and thus, that of the linear flow, is associated with a subsequent decrease in the rate of the cyclic flow. Under steady-state conditions of illumination, the contribution of cyclic flow to PSI turnover increases as a function of the light intensity (from 0 to ∼50% for weak to saturating light, respectively). Lack of CO 2 is associated with an increase in the efficiency of the cyclic flow. ATP concentration could be one of the parameters that control the transition between linear and cyclic modes.

Research paper thumbnail of Mechanism of electron transfer in the cytochrome b/f complex of algae: evidence for a semiquinone cy

The most widely accepted mechanism of electron and proton transfer within the cytochrome (Cyt) b/... more The most widely accepted mechanism of electron and proton transfer within the cytochrome (Cyt) b/f complex derives from the Q-cycle hypothesis originally proposed for the mitochondrial Cyt b/c1 complex by Mitchell [Mitchell, P. (1975) FEBS Lett. 57, 135-137]. In chloroplasts, the Cyt b/f complex catalyzes the oxidation of a plastoquinol at a site, Qo (the plastoquinol binding site), close to the inner aqueous phase and the reduction of a quinone at a site, Qi (the plastoquinone binding site), close to the stromal side of the membrane. In an alternative model, the semiquinone cycle [Wikström, M. & Krab, K. (1986) J. Bioenerg. Biomembr. 18, 181-193], a charged semiquinone formed at site Qo is transferred to site Qi where it is reduced into quinol. Flash-induced kinetics of the redox changes of Cyt b and of the formation of a transmembrane potential have been measured in Chlorella sorokiniana cells incubated in reducing conditions that induce a full reduction of the plastoquinone pool. The experiments were performed in the presence of an uncoupler that collapses the permanent electrochemical proton gradient and thus accelerates the rate of the electrogenic processes. The results show that the electrogenic reaction driven by the Cyt b/f complex precedes the processes of reduction or oxidation of the b-hemes. This electrogenic process is probably due to a transmembrane movement of a charged semiquinone, in agreement with the semiquinone-cycle hypothesis. This mechanism may represent an adaptation to reducing conditions when no oxidized quinone is available at the Qi site.

Research paper thumbnail of Period-four oscillations of the flash-induced oxygen formation in photosynthesis

Photosynthesis research, 2003

In this minireview, the earlier researches that led to the discovery of the period-four oscillati... more In this minireview, the earlier researches that led to the discovery of the period-four oscillations of the flash-induced oxygen formation are presented. It also includes the background of the classical model proposed by Bessel Kok, in which the formation of oxygen requires the sequential accumulation of four positive charges on the donor side of the same reaction center.

Research paper thumbnail of Mechanism of electron transfer in the cytochrome b/f complex of algae: evidence for a semiquinone cycle

Proceedings of the National Academy of Sciences of the United States of America, 1994

The most widely accepted mechanism of electron and proton transfer within the cytochrome (Cyt) b/... more The most widely accepted mechanism of electron and proton transfer within the cytochrome (Cyt) b/f complex derives from the Q-cycle hypothesis originally proposed for the mitochondrial Cyt b/c1 complex by Mitchell [Mitchell, P. (1975) FEBS Lett. 57, 135-137]. In chloroplasts, the Cyt b/f complex catalyzes the oxidation of a plastoquinol at a site, Qo (the plastoquinol binding site), close to the inner aqueous phase and the reduction of a quinone at a site, Qi (the plastoquinone binding site), close to the stromal side of the membrane. In an alternative model, the semiquinone cycle [Wikström, M. & Krab, K. (1986) J. Bioenerg. Biomembr. 18, 181-193], a charged semiquinone formed at site Qo is transferred to site Qi where it is reduced into quinol. Flash-induced kinetics of the redox changes of Cyt b and of the formation of a transmembrane potential have been measured in Chlorella sorokiniana cells incubated in reducing conditions that induce a full reduction of the plastoquinone pool....

Research paper thumbnail of Dissipation in bioenergetic electron transfer chains

Photosynthesis Research, 1996

This paper examines the processes by which wasteful dissipation of free energy may occur in bioen... more This paper examines the processes by which wasteful dissipation of free energy may occur in bioenergetic electron transfer chains. Frictionless transfer requires high rate constants in order to achieve a quasi-equilibrium steady-state. Previous results concerning the maximum power available from a photochemical source are recalled. The energetic performance of the bacterial reaction center is discussed, characterizing the processes that decrease either the quantum yield (recombination and obstruction) or the chemical potential (friction and non-equilibrated mechanisms). Considering the whole chain, diffusive carriers are potentially weaker links, due to kinetic limitation and short-circuiting reactions. It is suggested that the evolutionary trend has been to limit their number by lumping them into tightly bound protein complexes or, in a more flexible way, into labile supercomplexes.

Research paper thumbnail of Advances in photosynthesis and respiration : Including bioenergy and related processes: a new look beginning with volume 35

Photosynthesis research, 2012

This review provides a brief historical account of how microscopical studies of chloroplasts have... more This review provides a brief historical account of how microscopical studies of chloroplasts have contributed to our current knowledge of the structural and functional organization of thylakoid membranes. It starts by tracing the origins of the terms plastid, grana, stroma and chloroplasts to light microscopic studies of 19th century German botanists, and then describes how different types of electron microscopical techniques have added to this field. The most notable contributions of thin section electron microscopy include the elucidation of the 3-D organization of thylakoid membranes, the discovery of prolamellar bodies in etioplasts, and the structural changes in thylakoid architecture that accompany the light-dependent transformation of etioplasts into chloroplasts. Attention is then focused on the roles that freeze-fracture and freeze-etch electron microscopy and immuno electron microscopy have played in defining the extent to which the functional complexes of thylakoids are non-randomly distributed between appressed, grana and non-appressed stroma thylakoids. Studies reporting on how this lateral differentiation can be altered experimentally, and how the spatial organization of functional complexes is affected by alterations in the light environment of plants are also included in this discussion. Finally, the review points to the possible uses of electron microscope tomography techniques in future structural studies of thylakoid membranes.

Research paper thumbnail of Flash-induced oxidation of cytochrome b-563 in algae under anaerobic conditions: Effect of dinitrophenylether of iodonitrothymol

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1987

ABSTRACT

Research paper thumbnail of Supramolecular membrane protein assemblies in photosynthesis and respiration

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1993

Research paper thumbnail of The pH dependence of the redox midpoint potential of the 2Fe2S cluster from cytochrome b6f complex (the ‘Rieske centre’)

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1992

... 4()265 Rapid Report The pH dependence of the redox midpoint potential of the 2Fe2S cluster fr... more ... 4()265 Rapid Report The pH dependence of the redox midpoint potential of the 2Fe2S cluster from cytochrome b6f complex(the 'Rieske centre') Wolfgang Nitschke ~', Pierre Joliot ~', Ursula Liebl h A. William Rutherford h Giinter Hauska ~, Adolf Miiller J ... Healhcote+ P. and Moss. ...

Research paper thumbnail of Electron transfer between the two photosystems. I. Flash excitation under oxidizing conditions

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1984

ABSTRACT

Research paper thumbnail of Proton pumping and electron transfer in the cytochrome bf complex of algae

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1986

ABSTRACT

Research paper thumbnail of Excitation transfer between photosynthetic units: the 1964 experiment

Photosynthesis research, 2003

We review here the background and the experiments that led to the concept of excitation energy tr... more We review here the background and the experiments that led to the concept of excitation energy transfer among photosystem (PS) II units. On the basis of a kinetic analysis of oxygen evolution and chlorophyll a fluorescence yield, the authors showed, in 1964, that the PS II photochemical reaction involved in the formation of oxygen is not a first-order process. We concluded that excitation energy localized in a 'photosynthetic unit' including a reduced primary acceptor is transferred with a high probability to neighboring PS II units. Here, the beginnings and the original data of this topic are presented.

Research paper thumbnail of Supramolecular organization of the photosynthetic chain in chromatophores and cells of Rhodobacter sphaeroides

Photosynthesis Research, 1996

Flash-induced kinetics of the membrane potential increase related to electron transfer within the... more Flash-induced kinetics of the membrane potential increase related to electron transfer within the cytochrome (cyt) b/c1 complex (Phase III) and that of cyt c1+c2 reduction have been measured as a function of myxothiazol concentration in isolated chromatophores and whole cells of Rhodobacter sphaeroides. Upon addition of nonsaturating concentrations of myxothiazol, kinetics of Phase III display two phases, Phase IIIa and Phase IIIb. The amplitude of Phase IIIa, completed in about 10 ms, is proportional to the fraction of non-inhibited cyt b/c1 complexes, while its half-time is independent of the myxothiazol concentration. A fast cyt c1+c2 reduction phase is correlated to Phase IIIa. These experiments demonstrate that, in a range of time of several ms, diffusion of cyt c2 is restricted to domains formed by a supercomplex including two reaction centers (RCs) and a single cyt b/c1 complex, as proposed by Joliot et al. (Biochim Biophys Acta 975: 336-345, 1989). Phase IIIb, completed in about 100 ms, shows that positive charges or inhibitor molecules are exchanged between supercomplexes in this range of time. These exchanges occur within domains including 2 to 3 supercomplexes, i.e. in membrane domains smaller than a single chromatophore. These conclusions apply to both isolated chromatophores and whole cells.

Research paper thumbnail of COMPARAISON ENTRE L'EMISSION D'OXYGENE ET L'EMISSION DE LUMINESCENCE A LA SUITE D'UNE SERIE D'ECLAIRS SATURANTS

Photochemistry and Photobiology, 1970

ABSTRACT Abstract— Luminescence of Chlorella cells has been measured after illumination by a seri... more ABSTRACT Abstract— Luminescence of Chlorella cells has been measured after illumination by a series of short saturating flashes.The intensity of luminescence is strongly dependent upon the number of flashes; luminescence is minimum after a single flash and maximum after a double flash illumination.Ifl/n is the intensity of luminescence measured 0.24 sec after the nth flash, the series ln shows oscillations as a function of n. The series ln is very similar to the series yn, in which y is the amount of oxygen evolved by the nth flash, the term ln corresponding to the term yn+1. To interpret the oscillations of the series yn, different models of system II photochemical centers have been proposed, one by ourselves and the other one by KOK et al. In these models the electron donor Z of photosystem 11 is supposed to have 2 or 4 levels of oxidation, the more oxidized state being the precursor of oxygen. These different oxidation states of the donor Z allow storage of the photic energy in the system. The correlation between the series yn and ln shows that at least one of the oxidized forms of the donor Z is a substrate for the luminescence reaction.

Research paper thumbnail of Glu78, from the Conserved PEWY Sequence of Subunit IV, Has a Key Function in Cytochrome b 6 f Turnover †

Biochemistry, 1998

We have investigated the structure to function relationship at the Qo site in cytochrome b6f comp... more We have investigated the structure to function relationship at the Qo site in cytochrome b6f complexes in vivo. To this end, we created site-directed mutants of Chlamydomonas reinhardtii, at position 78 in the sequence of subunit IV. The target glutamic acid, present in the highly conserved 77PEWY80 sequence, was changed to residues of different polarities which did not prevent the functional assembly of cytochrome b6f complexes. Spectroscopic analysis performed in anaerobic conditions in vivo revealed distinct alterations in cytochrome b6f function, depending on the nature of the substituted residue. The semiconservative E78D substitution, in which only the length of the side chain is reduced, retained the functional features of the wild-type configuration. The E78K and E78L substitutions caused a significant decrease, by factors of 3 and 5, respectively, in the rate of the concerted oxidation process at the Qo site without a change in the affinity of Qo for reduced plastoquinones. The E78Q and E78N substitutions modified the characteristics of cytochrome b6f turnover under repetitive flash illumination. They caused a large increase in the electrogenicity of the electron-transfer reactions through the mutated cytochrome b6f complex. This increase was specifically sensitive to the electrical component of the proton-motive force. Surprisingly, despite the larger number of charges translocated across the membrane per charge injected in the high potential chain, the reduction phase for cytochrome b6 became barely detectable in the mutants, unless inhibitors at the Qi site were present. We show that similar functional characteristics can be observed with the cytochrome b6f complex in the wild-type in anaerobic conditions, provided a single flash illumination regime is used. These observations suggest that cytochrome b6f turnover may involve a mechanism implying an extra proton pumping activity.

Research paper thumbnail of On the advantages of using green light to study fluorescence yield changes in leaves

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2007

In photosynthetic chains, the kinetics of fluorescence yield depends on the photochemical rates a... more In photosynthetic chains, the kinetics of fluorescence yield depends on the photochemical rates at the level of both Photosystem I and II and thus on the absorption cross section of the photosynthetic units as well as on the coupling between light harvesting complexes and photosynthetic traps. A new set-up is described which, at variance with the commonly used set-ups, uses of a weakly absorbed light source (light-emitting diodes with maximum output at 520 nm) to excite the photosynthetic electron chain and probe the resulting fluorescence yield changes and their time course. This approach optimizes the homogeneity of the exciting light throughout the leaf and we show that this homogeneity narrows the distribution of the photochemical rates. Although the exciting light is weakly absorbed, the possibility to tune the intensity of the light emitting diodes allows one to reach photochemical rates ranging from 10 4 s − 1 to 0.25 s − 1 rendering experimentally accessible different functional regimes. The variations of the fluorescence yield induced by the photosynthetic activity are qualitatively and quantitatively discussed. When illuminating dark-adapted leaves by a weak light, the kinetics of fluorescence changes displays a pronounced plateau which precedes the fluorescence increase reflecting the full reduction of the plastoquinone pool. We ascribe this plateau to the time delay needed to reduce the photosystem I electron acceptors.

Research paper thumbnail of Equilibration between cytochrome f and P700 in intact leaves

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2005

Electron transport between the two photosynthetic reaction centres of high plants is mediated by ... more Electron transport between the two photosynthetic reaction centres of high plants is mediated by plastoquinone, a rieske iron-sulfur centre, cytochrome f and plastocyanin. Measurements of redox equilibration amongst these have produced confusing results, with apparent equilibrium constants being estimated that are inconsistent with in vitro measurements of redox midpoint potentials of the components concerned.

Research paper thumbnail of Fast oxidation of the primary electron acceptor under anaerobic conditions requires the organization of the photosynthetic chain of in supercomplexes

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2005

The kinetics of reoxidation of the primary acceptor Q a has been followed by measuring the change... more The kinetics of reoxidation of the primary acceptor Q a has been followed by measuring the changes in the fluorescence yield induced by a series of saturating flashes in intact cells of Rhodobacter sphaeroides in anaerobic conditions. At 0 8C, about half of Q a À is reoxidized in about 200 ms while reoxidation of the remaining fraction is completed in several seconds to minutes. The fast phase is associated with the transfer of ubiquinone formed at site Q o of the cytochrome bc 1 complex while the slowest phase is associated with the diffusion of ubiquinone present in the membrane prior to the flash excitation. The biphasic kinetics of Q a À oxidation is interpreted assuming that the electron chain is organized in supercomplexes that associate two RCs and one cyt bc 1 complex, which allows a fast transfer of quinone formed at the level of cyt bc 1 complex to the RCs. In agreement with this model, the fast phase of Q a À reoxidation is inhibited by myxothiazol, a specific inhibitor of cyt bc 1 . The PufX-deleted mutant displays only the slowest phase of Q a À oxidation; it is interpreted by the lack of supramolecular organization of the photosynthetic chain that leads to a larger average distance between cyt bc 1 and RCs. D

Research paper thumbnail of Slow electrogenic phase and intersystem electron transfer in algae

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1985

ABSTRACT

Research paper thumbnail of Flash-induced 519 nm absorption change in green algae

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1974

... Printed in The Netherlands BBA 46772 FLASHINDUCED 519 nm ABSORPTION CHANGE IN GREEN ALGAE PIE... more ... Printed in The Netherlands BBA 46772 FLASHINDUCED 519 nm ABSORPTION CHANGE IN GREEN ALGAE PIERRE JOLIOT and RENE DELOSME lnstitut de ... On the other hand, Nam HaiChua and Levine [6] observed that this mutant displays an abnormally large 520 nm ...

Research paper thumbnail of Cyclic electron flow in C3 plants

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2006

This paper summarized our present view on the mechanism of cyclic electron flow in C3 plants. We ... more This paper summarized our present view on the mechanism of cyclic electron flow in C3 plants. We propose that cyclic and linear pathways are in competition for the reoxidation of the soluble primary PSI acceptor, Ferredoxin (Fd), that freely diffuses in the stromal compartment. In the linear mode, Fd binds ferredoxin-NADP-reductase and electrons are transferred to NADP + and then to the Benson and Calvin cycle. In the cyclic mode, Fd binds a site localized on the stromal side of the cytochrome b 6 f complex and electrons are transferred to P 700 via a mechanism derived from the Q-cycle. In dark-adapted leaves, the cyclic flow operates at maximum rate, owing to the partial inactivation of the Benson and Calvin cycle. For increasing time of illumination, the activation of the Benson and Calvin cycle, and thus, that of the linear flow, is associated with a subsequent decrease in the rate of the cyclic flow. Under steady-state conditions of illumination, the contribution of cyclic flow to PSI turnover increases as a function of the light intensity (from 0 to ∼50% for weak to saturating light, respectively). Lack of CO 2 is associated with an increase in the efficiency of the cyclic flow. ATP concentration could be one of the parameters that control the transition between linear and cyclic modes.