Further Studies of Proton Translocations in Chloroplasts After Single-Turnover Flashes. I. Proton Uptake

1983 ◽  
Vol 10 (5) ◽  
pp. 363 ◽  
Author(s):  
AB Hope ◽  
DB Matthews
Keyword(s):  
Ionic Strength ◽  
Electron Flow ◽  
External Solution ◽  
Half Time ◽  
Cycle Model ◽  
Single Turnover ◽  
Q Cycle ◽  
Proton Uptake ◽  
Factor Α ◽  
Light Flashes

Damped, binary oscillations were observed in proton uptake by class C pea chloroplasts given a train of light flashes. The oscillation at pH 7.8 is predictable if the species accepting protons is either the doubly reduced secondary acceptor B�- or a plastoquinone PQ- from the pool, if 0.29 of the secondary acceptor is B- in dark-adapted chloroplasts and if a miss factor α = 0.12 governs the amval of electrons at B or B- after a flash. The rate of proton uptake was measured with varied pH, ionic strength and temperature. The half-time was 95 ms at pH 7.8 and 21°C. Using double flashes separated by variable intervals showed that the species able to accept protons was generated (t½) about 0.8 ms after a flash. The results are consistent with protons from the external solution reacting relatively slowly with univalent anions, which have earlier promptly supplied protons to B2- or PQ2-. Under conditions of cyclic and of non-cyclic electron flow, H+/e- stoichiometries were 1.1 and 1.0 respectively, and so the results do not support a Q-cycle model for pea chloroplasts.

Further Studies of Proton Translocations in Chloroplasts After Single-Turnover Flashes. III. Conditions for the Operation of an Apparent Q-Cycle in Thylakoids

1985 ◽  
Vol 12 (4) ◽  
pp. 387 ◽  
Author(s):  
AB Hope ◽  
L Handley ◽  
DB Mathews
Keyword(s):  
Electric Field ◽  
Electron Acceptor ◽  
Electron Flow ◽  
Cytochrome B6 ◽  
Single Turnover ◽  
Ph Values ◽  
Maximal Stimulation ◽  
Q Cycle ◽  
Proton Uptake ◽  
Transverse Electron

The proton-to-electron ratio in pea thylakoids, considering proton uptake with ferricyanide as electron acceptor, was reconfirmed as 1 in periods of single-turnover (<0.5 �s, 2-3 mJ) flashes delivered at 5-50 Hz and at pH values 6.4-8.3. Addition of valinomycin in the presence of K+ increased proton uptake in a way depending on [val], flash frequency and flash number. A maximal stimulation by valinomycin of up to about 1.8× controls was observed in fresh preparations. Half-maximal stimulation was caused by c. 2 nM valinomycin at 10-20 Hz, at c. 3 Hz with 10 nM valinomycin, and after c. five flashes at 50 Hz with 10 nM valinomycin. The results are discussed in terms of recent models for the Q-cycle. It is suggested that such a cycle operates in chloroplasts only when the intramembrane electric field induced in a series of flashes is kept small by the presence of valinomycin. Preliminary observations of 'P518', the thylakoid component probably indicating the electric field, are consistent with this idea. This field may control the transverse electron flow between the two cytochrome b6 molecules in the b/f complexes.

Further Studies of Proton Translocations in Chloroplasts After Single-Turnover Flashes. II. Proton Deposition

1984 ◽  
Vol 11 (4) ◽  
pp. 267 ◽  
Author(s):  
AB Hope ◽  
DB Matthews
Keyword(s):  
Electron Acceptor ◽  
Water Oxidation ◽  
Electron Flow ◽  
Neutral Red ◽  
S Phase ◽  
Cyclic Electron Flow ◽  
Slow Phase ◽  
Single Turnover ◽  
Q Cycle ◽  
Average Size

The deposition of protons in the inside spaces of pea class C chloroplasts was studied by means of the acidification of neutral red measured spectrophotometrically, with the outside space buffered. Careful kinetic analysis of such signals revealed three components, during non-cyclic electron flow induced by single-turnover flashes. These components included a 'slow' phase not emphasized in previous studies. The half-times of these phases were: 'Fast', < 1 ms (not resolved); 'Intermediate', 13-25 ms with added electron acceptor or 4 ms without; and 'Slow', 70-90 ms. Under conditions for cyclic electron flow only the I phase remained; it was the same magnitude as the I phase in non-cyclic flow, and its half-time was c. 3 ms. The F phase, which is usually attributed to protons from the oxidation of water, increased in average size with number of flashes (taken four flashes at a time) and was not fully patent until more than 20 flashes. The size of the I phase, which is usually attributed to protons from the oxidation of plastohydroquinone, when measured in a sequence of flashes to dark-adapted suspensions under non- cyclic conditions, had a binary oscillation in phase with the oscillation in proton uptake reported previously. It was concluded that protons leave PQH2 two at a time on alternate flashes. The S phase (average in 10 test flashes) was reduced by fast preflashes; an origin near photosystem II is suggested. The S phase may imply a small pool of proton-sequestering ability near the water oxidation site, or a number of other possibilities. In steady-state conditions, the ratio of the protons from PQH2 to those from water was 1.0 under all conditions examined except in the absence of added electron acceptor, when it was as high as 1.6. This was the only condition apparently indicating a Q-cycle, with infrequent single-turnover flashes.

Electron and Proton Transfers around the b/f Complex in Chloroplasts: Modelling the Constraints on Q-cycle Activity

1988 ◽  
Vol 15 (4) ◽  
pp. 567 ◽  
Author(s):  
AB Hope ◽  
DB Matthews
Keyword(s):  
Reduction Potential ◽  
Slow Phase ◽  
Single Turnover ◽  
Reduction Potentials ◽  
Q Cycle ◽  
Proton Transfers ◽  
Proton Uptake ◽  
Time Standard ◽  
Electron Transfers ◽  
Stimulation Of

The requirements for the operation of a Q-cycle in thylakoids are discussed. A computer model is described in which the state of reduction of components of the b/f complex is followed, single turnover at a time. Standard reduction potentials from the literature were assigned to the cytochrome b563 molecules; those for the second electron oxidation of plastoquinol at p-sites, and for the reduction of plastoquone at n-sites, were found by optimising the predicted stimulation of proton uptake by valinomycin. The stimulation has been attributed to uptake by doubly reduced plastoquinone at b/f complexes, a process thought to continue only if the membrane potential (ΔV) is kept low by ionophores. ΔV was simulated in the model via the electrochromic signal; its effect on electron transfers in the b/f complex was incorporated by modifying the reduction potentials. The extent of valinomycin stimulation of proton uptake, its dependence on [valinomycin] and flash frequency, the slow phase of the electrochromic signal and the extent of cytochrome b reduction were predicted by the model when the standard reduction potential for the p-site was set at -0.05 to -0.08 V. with that for the n-site at about 0 V.

Inhibition of oxygen evolution by ivalin

1994 ◽  
Vol 72 (2) ◽  
pp. 177-181 ◽  
Author(s):  
Ernesto Bernal-Morales ◽  
Alfonso Romo De Vivar ◽  
Bertha Sanchez ◽  
Martha Aguilar ◽  
Blas Lotina-Hennsen
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Sesquiterpene Lactone ◽  
Oxygen Evolution ◽  
Electron Flow ◽  
Atp Synthesis ◽  
Naturally Occurring ◽  
Transport Inhibitor ◽  
Proton Uptake ◽  
Key Words Oxygen

The inhibition of ATP synthesis, proton uptake, and electron transport (basal, phosphorylating, and uncoupled) from water to methylviologen by ivalin (a naturally occurring sesquiterpene lactone in Zaluzania triloba and Iva microcephala) indicates that it acts as electron transport inhibitor. Since photosystem I and electron transport from DPC to QA were not affected, while the electron flow of uncoupled photosystem II from H2O to DAD and from water to silicomolybdate was inhibited, we concluded that the site of inhibition of ivalin is located at the oxygen evolution level. Key words: oxygen evolution, ivalin, photosynthesis, sesquiterpene lactone.

Photosystem I-abhängige Phosphorylierung isolierter Chloroplasten mit Ascorbat/2.6-Dichlorphenolindophenol als Elektronendonator und Methylviologen als Elektronenakzeptor / Photosystem I Dependent Phosphorylation of Isolated Chloroplasts with Ascorbate/2,6-Dichlorophenolindophenol as Electron Donor and Methylviologen as Electron Acceptor

1972 ◽  
Vol 27 (4) ◽  
pp. 445-455 ◽  
Author(s):  
Heinrich Strotmann ◽  
Christa Von Gösseln
Keyword(s):  
Electron Transport ◽  
Linear System ◽  
Photosystem I ◽  
Electron Acceptor ◽  
Electron Flow ◽  
Phosphorylation Site ◽  
Cyclic System ◽  
Atp Production ◽  
Proton Uptake ◽  
Isolated Chloroplasts

Photosystem I related phosphorylation of isolated chloroplasts was investigated with special reference to the stoichiometry between ATP production and electron transprt (ATP: 2e⊖). The system studied contained DCMU to inhibit electron flow from photosystem II, ascorbate and DPIP to supply electrons to photosystem I, and methylviologen as electron acceptor. The following results were obtained:1. Basal electron transport is stimulated by the addition of the phosphorylating system, indicating that phosphorylation is really coupled to non-cyclic electron flow. The ratio ATP: 2e⊖ is 1, when the increase of electron flow obtained by the addition of ADP and phosphate is correlated to phosphorylation. This ratio is constant upon varying several parameters including DPIP concentration and light intensity.2. In the absence of methylviologen a DPIP catalyzed cyclic phosphorylation takes place (cf. I. c.7, 11, 12). Phosphorylation is not increased by the addition of methylviologen, indicating that both, the cyclic DPIP mediated and the non-cyclic system are coupled to the same phosphorylation site and limited by the same reaction step.3. In the absence of oxygen a methylviologen supported cyclic phosphorylation occurs. Comparing optimum rates, phosphorylation under these conditions is about twice as high as in the noncyclic system. Therefore we conclude that two phosphorylation sites are involved in methylviologen catalyzed cyclic electron transport. This system is sensitive against trypsin treatment of the chloroplasts, whereas the linear system is not.4. The two cyclic systems as well as the non-cyclic system are coupled to reversible proton uptake. Furthermore the linear system exhibits an irreversible uptake of hydrogen ions, which is stoichiometric to electron flow. From the reversible and the irreversible components of the pH changes the ratio of the proton pump to electron transprt can be calculated. Under steady state conditions the ration H⨁ : e⊖ approaches 1.

scholarly journals The Capacitance of Skeletal Muscle Fibers in Solutions of Low Ionic Strength

1972 ◽  
Vol 59 (3) ◽  
pp. 347-359 ◽  
Author(s):  
P. C. Vaughan ◽  
J. N. Howell ◽  
R. S. Eisenberg
Keyword(s):  
Skeletal Muscle ◽  
Ionic Strength ◽  
Surface Membrane ◽  
Muscle Fibers ◽  
External Solution ◽  
Rectangular Pulse ◽  
Bathing Solution ◽  
Skeletal Muscle Fibers ◽  
Tubular System ◽  
Low Ionic Strength

The capacitance of skeletal muscle fibers was measured by recording with one microelectrode the voltage produced by a rectangular pulse of current applied with another microelectrode. The ionic strength of the bathing solution was varied by isosmotic replacement of NaCl with sucrose, the [K] [Cl] product being held constant. The capacitance decreased with decreasing ionic strength, reaching a value of some 2 µF/cm2 in solutions of 30 mM ionic strength, and not decreasing further in solutions of 15 mM ionic strength. The capacitance of glycerol-treated fibers did not change with ionic strength and was also some 2 µF/cm2. It seems likely that lowering the ionic strength reduces the capacitance of the tubular system (defined as the charge stored in the tubular system), and that the 2 µF/cm2 which is insensitive to ionic strength is associated with the surface membrane. The tubular system is open to the external solution in low ionic strength solutions since peroxidase is able to diffuse into the lumen of the tubules. Twitches and action potentials were also recorded from fibers in low ionic strength solutions, even though the capacitance of the tubular system was very small in these solutions. This finding can be explained if there is an action potential—like mechanism in the tubular membrane.

Further Studies of Proton Translocations in Chloroplasts After Single-Turnover Flashes. IV. Effects of Cytochrome b/f Complex Inhibitors on Proton Uptake and Cytochrome b6 Turnover

1987 ◽  
Vol 14 (1) ◽  
pp. 47 ◽  
Author(s):  
AB Hope ◽  
S Birch ◽  
DB Matthews
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Reduction Rate ◽  
Maximum Effect ◽  
Phenol Red ◽  
Cytochrome B6 ◽  
Oxidation Rates ◽  
Single Turnover ◽  
Proton Uptake ◽  
Reduction And Oxidation

The effects of the substances 2-n-heptyl- and 2-n-nonyl-4-hydroxyquinoline N-oxide (HQNO, NQNO), and antimycin A (AMA) on proton uptake stimulated by a 10-20 Hz train of single-turnover flashes given to pea thylakoids were investigated. Electron transport was from H2O to ferricyanide ('oxidising conditions') and the pH indicator of proton uptake was phenol red. All three of HQNO, NQNO and AMA inhibited proton uptake in control conditions, with concentrations (c½) for half-maximum effect of 1.7, 0.1 and 5 �M, respectively. The valinomycin-stimulated proton uptake, which has been attributed to Q-cycle activity in thylakoids, was more sensitive to HQNO and NQNO, with c½ of 0.6 and < 0.05 �M respectively. AMA had the same or less relative effect on proton uptake in the presence of valinomycin as in its absence. In oxidising conditions the maximum extent of flash-induced cytochrome (cyt) b6 reduction was 7-9% of the total present (which was 2 molecules/620 chlorophylls), as an average during 10 flashes, valinomycin being always added to reduce interference from the electrochromic effect. The average half- time for this reduction was 3.4 ms, while that for oxidation was 420 ms. The amount of cyt b6 reduced was increased by NQNO to a maximum of 14-19%, the c½ being 0.05 �M. Reduction and oxidation rates were both diminished by NQNO. In reducing conditions [electrons from duroquinol to methyl viologen, 3-(3,4-dichlorophenyl)-l,l- dimethylurea added to inhibit photosystem II], the cytochrome b6 was 12-16% reduced during flashes at 0.5-1 Hz, with half-times of 3.1 and 21 ms for reduction and oxidation, respectively. NQNO increased the percentage reduced to a maximum of 34-45, with a c½ of 0.05 �M. The diminution of the oxidation rate of cyt b6 was similarly related to [NQNO] but that of the reduction rate had a c½ of -1 �M. The findings on proton uptake are seen as consistent with HQNO and NQNO inhibiting at the Qc sites on cyt b/f complexes, at QB sites near photosystem II with less specificity and possibly at Q2 sites during the first few turnovers. Data for AMA indicated that it does not inhibit at Qc. Electron transport from H2O to methyl purple was more sensitive to NQNO for the first few turnovers (c½ 0.1 �M) than in the steady state (c½ - 1 �M).

Cyclic Electron Flow Around Photosystem II as Examined by Photosynthetic Oxygen Evolution Induced by Short Light Flashes

1997 ◽  
Vol 52 (3-4) ◽  
pp. 175-179 ◽  
Author(s):  
W. I. Gruszecki ◽  
K. Strzałka ◽  
A. Radunz ◽  
G. H. Schmid
Keyword(s):  
Photosystem Ii ◽  
Oxygen Evolution ◽  
Molecular Mechanisms ◽  
Electron Flow ◽  
Red Light ◽  
Cyclic Electron Flow ◽  
Photosynthetic Oxygen Evolution ◽  
Absorption Region ◽  
Photosynthetic Oxygen ◽  
Light Flashes

Abstract Photosynthetic oxygen evolution from photosystem II particles was analyzed as consequence of a train of short (5 μs) flashes of different light quality and different intensities to study cyclic electron flow around photosystem II. Damped oscillations of the amplitudes of O2-evolution corresponding to a flash sequence were fitted numerically and analyzed in terms of a nonhomogeneous distribution of misses, represented by the probability parameter αi. Application of red light, known to promote cyclic electron flow around photosystem II (Gruszecki et al., 1995) results in a considerable increase of all αi, indicating that at the molecular level the misses may be interpreted as resulting from a competition for the reduction of oxidized P680 between cyclic electron flow and the electron flow coming from the water splitting enzyme. In accordance with previous findings, application of light flashes of the spectrum covering the absorption region of carotenoids resulted in an inhibition of cyclic electron flow and a pronounced decrease of the level of the miss parameter. Possible molecular mechanisms for the activity control of this cyclic electron transport around photosystem II by carotenoids are discussed.

scholarly journals A Comparison of the Effects of Metabolic Inhibitors on Chloride Uptake and Photosynthesis In Chara Oorallina

1969 ◽  
Vol 22 (2) ◽  
pp. 351 ◽  
Author(s):  
FA Smith ◽  
KR West
Keyword(s):  
Comparative Study ◽  
Electron Flow ◽  
External Solution ◽  
Metabolic Inhibitors ◽  
Chloride Uptake ◽  
Low Concentrations ◽  
Carbonyl Cyanide ◽  
Chloride Influx

A comparative study has been made of the effects of four metabolic inhibitors on chloride uptake and photosynthetic 14C02 fixation by cells of O. corallina, and on oxygen evolution by chloropl<1sts isolated from the cells. Low concentrations of phlorizin and Dio-9 inhibited chloride uptake, but this was not accompanied by an inhibition of photosynthesis in vivo, and could not be correlated with the measured inhibition of electron flow in vitro. Low concentrations of imidazole stimulated the chloride influx in light, but there was again no effect on photosynthetic 14C02 fixation, although imidazole did uncouple electron flow in vitro. The effect of imidazole was dependent on the pH of the external solution. Increasing concentrations of carbonyl cyanide m-chlorophenylhydrazone progressively reduced the chloride influx and 14C02 fixation, and uncoupled electron flow in vitro. The work provides no evidence to support the view that chloride uptake is directly linked to electron flow rather than phosphorylation.

scholarly journals Electron transfer via cytochrome b6f complex displays sensitivity to Antimycin A upon STT7 kinase activation.

2022 ◽  
Author(s):  
Felix Buchert ◽  
Martin Scholz ◽  
Michael Hippler
Keyword(s):  
Electron Transfer ◽  
Electron Flow ◽  
Anaerobic Treatment ◽  
State Transitions ◽  
Antimycin A ◽  
Cytochrome B6f Complex ◽  
Cytochrome B6f ◽  
Q Cycle ◽  
B6f Complex

The cytochrome b6f complex (b6f) has been initially considered as the ferredoxin-plastoquinone reductase (FQR) during cyclic electron flow (CEF) with photosystem I that is inhibited by antimycin A (AA). The binding of AA to the b6f Qi-site is aggravated by heme-ci, which challenged the FQR function of b6f during CEF. Alternative models suggest that PROTON GRADIENT REGULATION5 (PGR5) is involved in a b6f-independent, AA-sensitive FQR. Here, we show in Chlamydomonas reinhardtii that the b6f is conditionally inhibited by AA in vivo and that the inhibition did not require PGR5. Instead, activation of the STT7 kinase upon anaerobic treatment induced the AA sensitivity of b6f which was absent in stt7-1. However, a lock in State 2 due to persisting phosphorylation in the phosphatase double mutant pph1;pbcp did not increase AA sensitivity of electron transfer. The latter required a redox poise, supporting the view that state transitions and CEF are not coercively coupled. This suggests that the b6f-interacting kinase is required for structure-function modulation of the Qi-site under CEF favoring conditions. We propose that PGR5 and STT7 independently sustain AA-sensitive FQR activity of the b6f. Accordingly, PGR5-mediated electron injection into an STT7-modulated Qi-site drives a Mitchellian Q cycle in CEF conditions.

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