scholarly journals Inhibition and uncoupling of photophosphorylation in isolated chloroplasts by organotin, organomercury and diphenyleneiodonium compounds

1974 ◽  
Vol 142 (1) ◽  
pp. 65-74 ◽  
Author(s):  
Angela S. Watling-Payne ◽  
Michael J. Selwyn
Keyword(s):  
Electron Transport ◽  
Organotin Compounds ◽  
O2 Evolution ◽  
Phenylmercuric Acetate ◽  
Low Concentrations ◽  
Hydrophobic Site ◽  
Carbonyl Cyanide ◽  
High Concentrations ◽  
Highly Hydrophobic ◽  
Isolated Chloroplasts

1. Trialkyltin, triphenyltin and diphenyleneiodonium compounds inhibited ADP-stimulated O2 evolution by isolated pea chloroplasts in the presence of phosphate or arsenate. Tributyltin and triphenyltin were the most effective inhibitors, which suggests a highly hydrophobic site of action. Phenylmercuric acetate was a poor inhibitor of photophosphorylation, which suggests that thiol groups are not involved. 2. Triethyltin was a potent uncoupler of photophosphorylation by isolated chloroplasts in media containing Cl-, but had little uncoupling activity when Cl- was replaced by NO3- or SO42-, which are inactive in the anion–hydroxide exchange. It is suggested that uncoupling by triethyltin is a result of the Cl-–OH- exchange together with a natural uniport of Cl-. Tributyltin, triphenyltin and phenylmercuric acetate had low uncoupling activity, probably because in these compounds the uncoupling activity is partially masked by inhibitory effects. 3. At high concentrations the organotin compounds caused inhibition of electron transport uncoupled by carbonyl cyanide m-chlorophenylhydrazone or NH4Cl. At these high concentrations the organotin compounds may be producing a detergent-like disorganization of the membrane structure. In contrast, diphenyleneiodonium sulphate inhibited uncoupled electron transport at low concentrations; however, this inhibition is less than the inhibition of photophosphorylation, which suggests that the compound also inhibits the phosphorylation reactions as well as electron transport. 4. The effects of these compounds on basal electron transport were complex and depended on the pH of the reaction media. However, they can be explained on the basis of three actions: inhibition of the phosphorylation reactions, uncoupling and direct inhibition of electron transport. 5. The inhibition of cyclic photophosphorylation in the presence of phenazine methosulphate by diphenyleneiodonium sulphate shows that it inhibits in the region of photosystem 1.

Interference by Herbicides with the Transmembrane Potential of Thylakoids

1987 ◽  
Vol 42 (6) ◽  
pp. 718-726 ◽  
Author(s):  
Donald E. Moreland ◽  
William P. Novitzky
Keyword(s):  
Electron Transport ◽  
Thylakoid Membrane ◽  
Transmembrane Potential ◽  
Proton Motive Force ◽  
Cyclic Electron Transport ◽  
Low Concentrations ◽  
High Concentrations ◽  
Proton Shuttling ◽  
Electrical Components ◽  
Spinach Thylakoids

Interferences expressed by herbicides classified as inhibitory uncouplers were measured on the induction and maintenance of ΔpH and ΔΨ, the chemical and electrical components, respectively. of the proton motive force (pmf) generated by light-induced cyclic electron transport in spinach thylakoids. Maintenance of the pmf is required for the synthesis of ATP. The inhibitory uncouplers arc known to inhibit photophosphorylation, but the mechanisms involved remain to be identified. The dinoseb types (dinitrophenols. benzimidazoles. benzonitriles. bromophenoxim. perfluidone. thiadiazoles) of inhibitory uncouplers, most of which contain dissociable protons, were found to discharge ΔpΗ at low concentrations and to collapse ΔΨ at high concentrations. Collapse of ΔpΗ can be attributed to the protonophoric (proton shuttling) action of the herbicides. However, collapse of ΔΨ can be caused by alterations induced to the integrity and loss of semipermeability of the thylakoid membrane. As a result the membrane bccomes permeable to protons and other cations, and the electrical charges across the membrane are neutralized. The non-ionic dicryl types of inhibitory uncouplers (acylanilides. dinitroanilines. diphenylethcrs. bis-carbamates) collapsed ΔΨ at concentrations that were somewhat lower than those required for the collapse of ΔpΗ. These herbicides appear only to alter the integrity and permeability of the thylakoid membrane. Inhibition of photophosphorylation by the inhibitory uncouplcrs correlated with their ability to dissipate the pmf.

scholarly journals The effects of high concentrations of salts on photosynthetic electron transport in spinach (Spinacia oleracea) chloroplasts

1982 ◽  
Vol 204 (3) ◽  
pp. 705-712 ◽  
Author(s):  
A C Stewart
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Spinacia Oleracea ◽  
Photosynthetic Electron Transport ◽  
Potassium Citrate ◽  
O2 Evolution ◽  
Hofmeister Series ◽  
Reaction Centre ◽  
High Concentrations

1. Photosynthetic electron transport from water to lipophilic Photosystem II acceptors was stimulated 3-5-fold by high concentrations (greater than or equal to 1 M) of salts containing anions such as citrate, succinate and phosphate that are high in the Hofmeister series. 2. In trypsin-treated chloroplasts, K3Fe(CN)6 reduction insensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea was strongly stimulated by high concentrations of potassium citrate, but there was much less stimulation of 2,6-dichloroindophenol reduction in Tris-treated chloroplasts supplied with 1,5-diphenylcarbazide as artificial donor. The results suggest that the main site of action of citrate was the O2-evolving complex of Photosystem II. 3. Photosystem I partial reactions were also stimulated by intermediate concentrations of citrate (up to 2-fold stimulation by 0.6-0.8 M-citrate), but were inhibited at the highest concentrations. The observed stimulation may have been caused by stabilizaton of plastocyanin that was complexed with the Photosystem I reaction centre, 4. At 1 M, potassium citrate protected O2 evolution against denaturation by heat or by the chaotropic agent NaNO3. 5. It is suggested that anions high in the Hofmeister series stimulated and stabilized electron transport by enhancing water structure around the protein complexes in the thylakoid membrane.

Effects of Atrazine, Cyanazine, and Procyazine on the Photochemical Reactions of Isolated Chloroplasts

Weed Science ◽  
1979 ◽  
Vol 27 (3) ◽  
pp. 300-308 ◽  
Author(s):  
P. E. Brewer ◽  
C. J. Arntzen ◽  
F. W. Slife
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Primary Electron ◽  
Fluorescence Induction ◽  
Photochemical Reactions ◽  
Time Dependent ◽  
Chlorophyll Fluorescence Induction ◽  
Transport Assay ◽  
Highly Hydrophobic ◽  
Isolated Chloroplasts

The effects of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile}, and procyazine {2-[[4-chloro-6-(cyclopropylamino)-1,3,5-triazine-2-yl] amino]-2-methylpropanenitrile} on the photochemical reactions of isolated pea (Pisum sativum L. ‘Progress #9 Dwarf’) chloroplasts were studied. Atrazine, cyanazine, and procyazine inhibited electron transport but did not uncouple photophosphorylation. The primary site of inhibition for all three herbicides was on the reducing side of photosystem II; the electron transfer step between the primary electron acceptor (Q) and the plastoquinone pool of the electron transport chain is suggested as the site of action of all three herbicides. The amount of inhibition of electron transport observed after addition of herbicide to isolated chloroplasts was time-dependent for cyanazine and procyazine but not for atrazine. This was apparently due to a slower partitioning of cyanazine and procyazine from the aqueous phase of the reaction solution into the highly hydrophobic environment within the chloroplast membrane. Treatment of the thylakoid membranes with detergent reduced the time-dependent inhibitory nature of cyanazine and procyazine, and the ability of atrazine to block electron transport. A photosystem II-dependent electron transport assay and a chlorophyll fluorescence induction assay were used to determine the inhibitory potentials of atrazine, cyanazine, and procyazine. After allowing for differences in the rate of membrane penetration, I50 values of approximately 2 × 10−7 M were determined for each of the three herbicides.

scholarly journals The effects of oxygen solubility and high concentrations of salts on photosynthetic electron transport in chloroplast membranes

1984 ◽  
Vol 218 (2) ◽  
pp. 539-545 ◽  
Author(s):  
B Thomasset ◽  
J N Barbotin ◽  
D Thomas
Keyword(s):  
Electron Transport ◽  
Photosynthetic Electron Transport ◽  
Potassium Citrate ◽  
Potassium Ferricyanide ◽  
O2 Evolution ◽  
Oxygen Solubility ◽  
Chloroplast Membranes ◽  
Ferricyanide Reduction ◽  
High Concentrations ◽  
Stimulation Of

Chloroplast membranes were isolated in different media containing Hepes [4-(2-hydroxyethyl)-1-piperazine-ethanesulphonic acid] and high concentrations of sorbitol (0.33 M), potassium citrate (0.75 M) or Na2SO4 (1.0 M). Due to the complexity of the media, the oxygen solubility is strongly modified by high concentrations of salts (oxygen solubility for 0.33 M-sorbitol, 0.21 mmol/litre; for 0.75 M-potassium citrate, 0.121 mmol/litre; and for 1.0 M-Na2SO4, 0.112 mmol/litre). The knowledge of these values is necessary to interpret the rate of O2 evolution. For thylakoids isolated in ‘sorbitol buffer’ and then tested in high concentrations of potassium citrate, a slight stimulation of O2 evolution is observed (143-173 mumol of O2/h per mg of chlorophyll a) with potassium ferricyanide as electron acceptor. When we monitor the potassium ferricyanide reduction, no stimulation of electron transport is obtained even if the observed phenomenon is identical with the Photosystem-II oxygen evolution. In the same experiments no stimulation of the photophosphorylation was recorded, but when thylakoids are directly isolated in 0.75 M-potassium citrate, O2 evolution, ferricyanide reduction and photophosphorylation are inhibited by high concentrations of salts. The behaviour of thylakoids seems to be influenced by their initial treatment.

scholarly journals Effects of Cadmium on Carbonic Anhydrase and Activities Dependent on Electron Transport of Isolated Chloroplasts.

1969 ◽  
Vol 63 (2) ◽  
pp. 195-201 ◽  
Author(s):  
Carmen I. Asencio ◽  
Arturo Cedeño-Maldonado
Keyword(s):  
Electron Transport ◽  
Carbonic Anhydrase ◽  
Co2 Fixation ◽  
Strong Inhibition ◽  
Enzyme Preparations ◽  
Low Concentrations ◽  
Intact Chloroplasts ◽  
Isolated Chloroplasts

Low concentrations of Cadmium inhibit the electron transport and CO2 fixation reactions of isolated chloroplasts. CO2 fixation is more sensitive to Cd than electron transport and dark pre-incubation increases the degree of toxicity to both. Carbonic anhydrase, an enzyme associated with CO2 fixation, is very sensitive to Cd either when applied directly to partially purified preparations of the enzyme or when enzyme preparations are obtained from intact chloroplasts previously exposed to Cd. Strong inhibition occurs at Cd concentrations lower than those required to inhibit any of the electron transport dependent reactions studied. These results are interpreted as evidence that carbonic anhydrase is one of the most sensitive sites of Cd action in isolated chloroplasts.

Effects of Potassium-(picrate)-(18-crown-6) on the Photosynthetic Electron Transport

1996 ◽  
Vol 51 (7-8) ◽  
pp. 539-547 ◽  
Author(s):  
L. Kovács ◽  
U. Hegde ◽  
S. Padhye ◽  
G. Bernát ◽  
S. Demeter
Keyword(s):  
Electron Transport ◽  
Photosynthetic Electron Transport ◽  
Fluorescence Yield ◽  
Charge Recombination ◽  
Electron Donors ◽  
Low Concentrations ◽  
Tyrosine Z ◽  
High Concentrations ◽  
Tyrosine D ◽  
Potassium Picrate

Abstract The effects of potassium-(picrate)-(18-crown-6) on the electron transport of photosystem II was investigated in isolated pea thylakoids. Low concentrations of the compound inhibited the fast decay of fluorescence yield associated with electron transfer between the primary (QA) and secondary (QB) quinone electron acceptor and increased the intermediary level of fluorescence to the Fmax level. The decay half-time of fluorescence yield measured in the presence of DCMU(S2QA- charge recombination) decreased from about 1.8 s to about 0.3 s in thylakoids treated with potassium-(picrate)-(18-crown-6). While the inhibition of electron transport by DCMU gave rise to the appearance of a thermoluminescence band at about + 10°C (S2QA- charge recombination) addition of potassium-(picrate)-(18-crown-6) resulted in a thermoluminescence band at about -10°C. Increasing concentrations of potassium-(picrate)-(18-crown-6) diminished the fluorescence yield and the -10°C TL band and abolished the Signal IIS and Signal IIf EPR signals of the tyrosine-D and tyrosine-Z electron donors, respectively. The phenolic-type inhibitor, potassium picrate had the same effect on thermoluminescence and on the tyrosine EPR signals. It is concluded that potassium-(picrate)-(18-crown-6) is a phenolic type inhibitor owing to its picrate constituent. At low concentrations picrate and potassium-(picrate)-18-crown) not only block the electron transport between QA and QB but they probably decrease the midpoint redox potential of QA, as well. At high concentrations they also inhibit the light-induced oxidation of the tyrosine-D and tyrosine-Z donors.

scholarly journals Photosynthetic electron transport in thylakoid preparations from two marine red algae (Rhodophyta)

1983 ◽  
Vol 210 (2) ◽  
pp. 583-589 ◽  
Author(s):  
A C Stewart ◽  
A W D Larkum
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Red Algae ◽  
Higher Plants ◽  
Outer Part ◽  
Photosynthetic Electron Transport ◽  
O2 Evolution ◽  
Blue Green Algae ◽  
High Concentrations

Thylakoid membrane preparations active in photosynthetic electron transport have been obtained from two marine red algae, Griffithsia monilis and Anotrichium tenue. High concentrations (0.5-1.0 M) of salts such as phosphate, citrate, succinate and tartrate stabilized functional binding of phycobilisomes to the membrane and also stabilized Photosystem II-catalysed electron-transport activity. High concentrations (1.0 M) of chloride and nitrate, or 30 mM-Tricine/NaOH buffer (pH 7.2) in the absence of salts, detached phycobilisomes and inhibited electron transport through Photosystem II. The O2-evolving system was identified as the electron-transport chain component that was inhibited under these conditions. Washing membranes with buffers containing 1.0-1.5 M-sorbitol and 5-50 mM concentrations of various salts removed the outer part of the phycobilisome but retained 30-70% of the allophycocyanin ‘core’ of the phycobilisome. These preparations were 30-70% active in O2 evolution compared with unwashed membranes. In the sensitivity of their O2-evolving apparatus to the composition of the medium in vitro, the red algae resembled blue-green algae and differed from other eukaryotic algae and higher plants. It is suggested that an environment of structured water may be essential for the functional integrity of Photosystem II in biliprotein-containing algae.

scholarly journals Hydrogen peroxide production in uncoupled mitochondria of the parasitic nematode worm Nippostrongylus brasiliensis

1987 ◽  
Vol 243 (2) ◽  
pp. 589-595 ◽  
Author(s):  
T A Paget ◽  
M Fry ◽  
D Lloyd
Keyword(s):  
Electron Transport ◽  
Parasitic Nematode ◽  
H2o2 Production ◽  
Nippostrongylus Brasiliensis ◽  
Antimycin A ◽  
Transport Pathway ◽  
Salicylhydroxamic Acid ◽  
Low Concentrations ◽  
Carbonyl Cyanide ◽  
Nematode Worm

1. Mitochondria from the parasitic nematode worm Nippostrongylus brasiliensis produce H2O2 in the energized state; higher rates of H2O2 production were observed in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone. 2. Antimycin A inhibits respiration and H2O2 production by 70 and 65% respectively; the residual activities can be attributed to alternative electron-transport pathway(s). 3. o-Hydroxydiphenyl and 1,3,5-trihydroxybenzene, inhibitors of alternative electron transport, inhibit respiration by 37% and H2O2 production by 26%. 4. Another inhibitor of alternative electron transport, salicylhydroxamic acid, shows a complex mode of action; low concentrations (less than 0.5 mM) stimulate respiration and H2O2 production, whereas 2 mM-salicylhydroxamic acid inhibited respiration by 35% and stopped H2O2 production completely. 5. O2 thresholds were observed for the inhibition of respiration at O2 concentrations greater than 57.7 microM and inhibition of H2O2 production (greater than 20.5 microM-O2); apparent Km values for oxygen were 5.5 microM and 3.0 microM respectively. 6. In the presence of antimycin A the O2-inhibition thresholds and apparent Km values for O2 of respiration and H2O2 production matched closely, suggesting that the alternative oxidase is a likely site of H2O2 production. 7. These results are discussed in relation to O2 toxicity to N. brasiliensis.

Neutrophil Elastase Potentiates Cathepsin G-lnduced Platelet Activation

1992 ◽  
Vol 68 (05) ◽  
pp. 570-576 ◽  
Author(s):  
Mary A Selak
Keyword(s):  
Neutrophil Elastase ◽  
Cell Activation ◽  
Thromboxane A2 ◽  
Creatine Phosphate ◽  
Dense Granule ◽  
Cathepsin G ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Low Concentrations ◽  
High Concentrations

SummaryWe have previously demonstrated that human neutrophil cathepsin G is a strong platelet agonist that binds to a specific receptor. This work describes the effect of neutrophil elastase on cathepsin G-induced platelet responses. While platelets were not activated by high concentrations of neutrophil elastase by itself, elastase enhanced aggregation, secretion and calcium mobilization induced by low concentrations of cathepsin G. Platelet aggregation and secretion were potentiated in a concentration-dependent manner by neutrophil elastase with maximal responses observable at 200 nM. Enhancement was observed when elastase was preincubated with platelets for time intervals of 10–60 s prior to addition of a low concentration of cathepsin G and required catalytically-active elastase since phenylmethanesulphonyl fluoride-inhibited enzyme failed to potentiate cell activation. Neutrophil elastase potentiation of platelet responses induced by low concentrations of cathepsin G was markedly inhibited by creatine phosphate/creatine phosphokinase and/or indomethacin, indicating that the synergism between elastase and cathepsin G required the participation of ADP and thromboxane A2. On the other hand, platelet responses were not attenuated by the PAF antagonist BN 52021, signifying that PAF-acether did not play a role in elastase potentiation. At higher concentrations porcine pancreatic elastase exhibits similar effects to neutrophil elastase, demonstrating that the effect of elastase was not unique to the neutrophil protease. While neutrophil elastase failed to alter the ability of cathepsin G to hydrolyze a synthetic chromogenic substrate, preincubation of platelets with elastase increased the apparent affinity of cathepsin G binding to platelets. In contrast to their effect on cathepsin G-induced platelet responses, neither neutrophil nor pancreatic elasatse potentiated aggregation or dense granule release initiated by ADP, PAF-acether, arachidonic acid or U46619, a thromboxane A2 mimetic. Moreover, unlike its effect on cathepsin G, neutrophil elastase inhibited thrombin-induced responses. The current observations demonstrate that elastase can potentiate platelet responses mediated by low concentrations of cathepsin G, suggesting that both enzymes may function synergistically to activate platelets under conditions where neutrophil degranulation occurs.

In Vitro Effects of Ethanol on Rabbit Platelet Aggregation, Secretion of Granule Contents, and Cyclic AMP Levels in the Presence of Prostacyclin

1989 ◽  
Vol 61 (02) ◽  
pp. 254-258 ◽  
Author(s):  
Margaret L Rand ◽  
Peter L Gross ◽  
Donna M Jakowec ◽  
Marian A Packham ◽  
J Fraser Mustard
Keyword(s):  
Cyclic Amp ◽  
Inhibitory Effect ◽  
Rabbit Platelet ◽  
Inhibitory Effects ◽  
Low Concentrations ◽  
Rabbit Platelets ◽  
High Concentrations ◽  
In Vitro Effects ◽  
Aggregation Of Platelets

SummaryEthanol, at physiologically tolerable concentrations, inhibits platelet responses to low concentrations of collagen or thrombin, but does not inhibit responses of washed rabbit platelets stimulated with high concentrations of ADP, collagen, or thrombin. However, when platelet responses to high concentrations of collagen or thrombin had been partially inhibited by prostacyclin (PGI2), ethanol had additional inhibitory effects on aggregation and secretion. These effects were also observed with aspirin- treated platelets stimulated with thrombin. Ethanol had no further inhibitory effect on aggregation of platelets stimulated with ADP, or the combination of ADP and epinephrine. Thus, the inhibitory effects of ethanol on platelet responses in the presence of PGI2 were very similar to its inhibitory effects in the absence of PGI2, when platelets were stimulated with lower concentrations of collagen or thrombin. Ethanol did not appear to exert its inhibitory effects by increasing cyclic AMP above basal levels and the additional inhibitory effects of ethanol in the presence of PGI2 did not appear to be brought about by further increases in platelet cyclic AMP levels.

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