Changes in the glutathione level induced by transplasma membrane electron transport in maize (Zea mays L.)

Summary We investigated changes of thiols (GSH, GSSG, and cysteine) induced by transplasma membrane electron transport after addition of artificial electron acceptors and the influence of the thiol level on redox activity. GSH, GSSG, and cysteine content of maize (Zea mays L. cv. Golden Bantam) roots and coleoptile segments was determined by high performance liquid chromatography with a fluorescence detector. GSSG increased after treatment with 0.8 mM diamide, an SH-group oxidizer. GSH level of roots increased after treatment with diamide, while GSH levels of coleoptiles decreased. Incubation of roots with the GSH biosynthesis inhibitor buthionine-D,L-sulfoximine for 6 days lowered the glutathione level up to 80%. However, the GSH/GSSG ratio of maize roots remained constant after treatment with both effectors. The GSH/GSSG ratio and the glutathione level were changed by addition of artificial electron acceptors like hexacyanoferrate (III) or hexabromoiridate (IV), which do not permeate the plasma membrane. Hexacyanoferrate (III) reduction was inhibited up to 25% after the cellular glutathione level was lowered by treatment with diamide or buthionine-D,L-sulfoximine. Proton secretion induced by reduction of the electron acceptors was not affected by both modulators. The change in glutathione level is different for roots and coleoptiles. Our data are discussed with regard to the role of GSH in electron donation for a plasma membrane bound electron transport system.Abbreviations Buthionine-D,L-sulfoximine s-n-butyl-homocysteine sulfoximine - cys cysteine - diamide 1,1-azobis (N,N-dimethyl-formamide) - DTE dithioerythritol - EDTA ethylenediaminetetraacetic acid - GSH reduced glutathione - GSSG oxidizied glutathione, glutathione disulfide - HBI IV hexabromoiridate (IV) (K₂[IrBr₆]) - HCF III hexacyanoferrate (III) (K₃[Fe(CN)₆] - NEM N-ethylmaleimide - PM plasma membrane - Tris Tris(hydroxymethyl)aminomethane     

The electron transport system of Alcaligenes eutrophus H16

The electron transport system of autotrophically grown Alcaligenes eutrophus H16 has been investigated by spectroscopic and thermodynamic approaches. The results have been interpreted as evidence that isolated membranes contain a branched respiratory chain composed of three c-type haems (E _m,7=+160 mV, + 170 mV, and + 335 mV), five b-type haems (E _m,7=+ 5 mV, + 75 mV, + 205 mV, + 300 mV, and + 405 mV), two (possibly three) a-type haems [E _m,7= + 255 mV, + 350 mV, (+ 420 mV)], and nne d-type haem. EPR-analysis of the signals at g=1.93, g=2.02, and g=1.90 revealed the presence of iron-sulphur centres diagnostic of complexes I (NADH dehydrogenase), II (succinate dehydrogenase), and III (ubiquinol/cytochrome c oxidoreductase). The low potential b haems (+ 5 mV and + 75 mV) plus the Rieske protein (g=1.90, E _m,7=+ 280 mV), thought to be part of an orthodox bc ₁ complex, were present in low amounts as compared to their counterparts in membranes from Paracoccus denitrificans.CO-difference spectra in the presence of either succinate, NADH, hydrogen, ascorbate/TMPD, and/or dithionite as reductants, suggested the existance of four different oxidases composed by bo-, cb-, a-, and d-type haems.It is concluded that in contrast to other chemolithotrophes, e.g. P. denitrificans, autotrophic growth of Alcaligenes eutrophus utilizes a respiratory system in which the bc ₁ complex containing pathway is only partially involved in electron transport.Abbreviations Cytochrome c-551, number wavelength in nm - Cytochrome c ₂₇₀, number mid-point potential in mV - E _m,7 mid-point potential of an oxidation-reduction couple at pH 7.0 - KP buffer, potassium phosphate-buffer - OD optical density at 436 nm, 1 cm light path - TMPD N,N,N,N-tetramethyl-p-phenylenediamine     

Inhibition of photosynthesis and respiration by batatasins

Effects of batatasins I, III and V, phenolic growth inhibitors occuring in dormant bulbils of Dioscorea batatas Decne., on photosynthetic reactions of chloroplasts from spinach (Spinacia oleracea L.) and on respiration of mitochondria from potatoes (Solanum tuberosum L.) were investigated. In chloroplasts, the batatasins effectively inhibited CO₂-dependent oxygen evolution and electron flow from water to acceptors such as dichlorophenolindophenol, ferricyanide and methylviologen. Photosystem-I dependent electron transport from ascorbate to oxygen was stimulated. The proton conductivity of thylakoid membranes was increased and phosphorylation was uncoupled from electron transport. Inhibition of electron transport with water as electron donor appeared to precede uncoupling. In mitochondrial, batatasin I did not much inhibit succinate-dependent O₂ uptake in the absence of ADP, but caused strong inhibition in the presence of ADP. Batatasins III and V inhibited oxygen uptake irrespective of the presence or absence of ADP. Inhibition of chloroplast and mitochondrial reactions by batatasins was shown to be reversible.Abbrevations B-I batatasin I, 6-hydroxy-2,4,7-trimethoxyphenanthrene - B-III batatasin III, 3,3-dihydroxy-5-methoxybibenzyl - B-V batatasin V, 2-hydroxy-3,4,5-trimethoxybibenzyl - Chl chlorophyll - MV methylviologen - DCPIP 2,6-dichlorophenol-indophenol - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PVP polyvinylpyrrolidone     

Adenylate regulation of photosynthetic electron transport and the coupling sites of phosphorylation in spinach chloroplasts

The regulation by adenylates of activities of various partial electron transport systems in spinach chloroplasts was studied using systems from H₂O to 2,5-dimethyl-p-benzoquinone, H₂O to 2,6-dichlorophenolindophenol, reduced 2,6-dichlorophenolindophenol to methyl viologen, and H₂O to methyl viologen or ferricyanide. Adenylates regulated all of them. The ratio of the amount of esterified Pi (P) to that of electrons transported (e) in coupling with phosphorylation manifested that there are two phosphorylation sites: one between H₂O and 2,5-dimethyl-p-benzoquinone or 2,6-dichlorophenolindophenol and another between reduced 2,6-dichlorophenolindophenol and methyl viologen, under the proposed stoichiometries,i.e., P/H⁺=0.5 and H⁺/e=1, where H⁺ is the amount of protons pumped by electron transport (= those translocated during phosphorylation), when the basal electron transport (the part not regulated by adenylates) was excluded. The effects of pH, phlorizin, and methylamine on the adenylate regulation of electron transport, and the stimulation profile of electron transport coupled with quasiarsenylation suggested no distinction between the two phosphorylation sites.     

Noncyclic electron transport in chromatophores from photolithotrophically grown Rhodobacter sulfidophilus

Chromatophores isolated from the marine phototrophic bacterium Rhodobacter sulfidophilus were found to photoreduce NAD with sulfide as the electron donor. The apparent K _m for sulfide was 370 M and the optimal pH was 7.0. The rate of NAD photoreduction in chromatophore suspensions with sulfide as the electron donor (about 7–12 M/h·mol Bchl) was approximately onetenth the rate of sulfide oxidation in whole cell suspensions. NAD photoreduction was inhibited by rotenone, carbonyl cyanide-m-chlorophenylhydrazone, and antimycin A. Sulfide reduced ubiquinone in the dark when added to anaerobic chromatophore suspensions. These results suggest that electron transport from sulfide to NAD involves an initial dark reduction of ubiquinone followed by reverse electron transport from ubiquinol to NAD mediated by NADH dehydrogenase.Abbreviations Bchl bacteriochlorophyll - CCCP carbonyl cyanide-m-chlorophenylhydrazone - MOPS 3(N-morpholino)-propane sulfonate - Uq ubiquinone     

On the rates of cyclic electron transport around Photosystem II in the presence of donor side limitation

Photosystem II cyclic electron transport was investigated at low pH in spinach thylakoids and PS II preparations from the cyanobacteriumPhormidium laminosum. Variable fluorescence (F_v) quenching at a very low light intensity was examined as an indicator of cyclic electron flow. A progressive quenching of F_v was observed as the pH was lowered; however, this was shown to be mainly due to an inhibition of oxygen evolution. Cyclic electron flow in the uninhibited centres was estimated to occur at a rate comparable to or smaller than 1 mole O₂ mg Chl^–1 h^–1 in the pH range 5.0 to 7.8.The quantum yeeld of oxygen production is known to decrease at low pH and has been taken to indicate cyclic electron flow (Crofts and Horton (1991) Biochim Biophys Acta 1058: 187–193). However, a direct all-or-none inhibition of oxygen production at low pH has also been reported (Meyer et al. (1989) Biochim Biophys Acta 974: 36–43). We have analysed the effects of light intensity on the rates of oxygen evolution in order to calculate _U, the quantum yield of open and uninhibited centres. _U was found to be constant over a broad pH range, and by using ferricyanide and phenyl-p-benzoquinone as electron acceptors the maximum possible rate of cyclic electron transport was equivalent to no more than 1 mole O₂ mg Chl^–1 h^–1. The rate was no greater when the acceptor was adjusted to provide the most favourable conditions for cyclic flow.     

Effects of inorganic carbon accumulation on photosynthetic oxygen reduction and cyclic electron flow in the cyanobacterium Synechococcus PCC7942

This paper examines the effect of inorganic carbon transport and accumulation in Synechococcus PCC7942 on fluorescence quenching, photosynthetic oxygen reduction and both linear and cyclic electron flow. The data presented support the previous findings of Miller et al. (1991) that the accumulation of Ci by the CO₂ concentrating mechanism is able to stimulate oxygen photoreduction, particularly so when CO₂ fixation is inhibited by PCR cycle inhibitors such as glycolaldehyde. This effect is found with both high and low-Ci grown cells, but the potential for oxygen photoreduction is about two-fold higher in low-Ci grown cells. This greater potential for O₂ photoreduction is also correlated with a higher ability of low-Ci cells to photoreduce H₂O₂. Experiments with a mutant which transports Ci but does not accumulate it internally, indicates that the stimulation of O₂ photoreduction appears to be a direct effect of the internal accumulation of Ci rather than from its participation in the transport process. In the absence of Ci, no specific partial reactions of photosynthetic electron transport appear to be inhibited, and the PS 1 acceptors PNDA and MV as well as the PS 2 acceptor DMQ can all run electron transport at levels approaching those during active CO₂ fixation. Measurements of P700⁺ show that when the cells are depleted of Ci during photosynthesis, P700 becomes more oxidised. This indicates that the resupply of electrons from the intersystem chain is relatively more restricted under conditions of Ci limitation than is the availability of PS 1 electron acceptors. It is proposed that the accumulated Ci pool can directly stimulate the ability of O₂ to act as a PS 1 acceptor and that the ability of PS 1 acceptors, such as O₂, to relieve restrictions on intersystem electron transfer is perhaps a result of a reduction in cyclic electron flow and a subsequent increase in the oxidation state of the plastoquinone pool.Abbreviations BTP 1,3-bis[tris(hydroxymethyl)-methylaminopropane] - CA carbonic anhydrase' - Ci inorganic carbon (CO₂+HCO₃ ^–+CO₃ ^2–) - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DMQ 2,6-dimethylbenzoquinone - EZ ethoxyzolamide or 6-ethoxy-2-benzothiazole-sulfonamide - FCCP carbonyl cyanide p-trifluoro methoxyphenyl-hydrazone - F steady-state chlorophyll fluorescence - F_m chlorophyll fluorescence during a saturating light pulse - F_o chlorophyll fluorescence in the dark, prior to illumination by actinic light - MV methyl viologen or 1,1-dimethyl-4,4-bipyridinium dichloride - PCR cycle photosynthetic carbon reduction cycle - PNDA N,N-dimethyl-p-nitrosoaniline - _{PS 1} the quantum yield of Photosystem 1 - _{PS 2} the quantum yield of Photosystem 2     

Regulation of anaerobic respiratory pathways in Wolinella succinogenes by the presence of electron acceptors

In Wolinella succinogenes ATP synthesis and consequently bacterial growth can be driven by the reduction of either nitrate (E₀=+0.42 V), nitrite (E₀=+0.36 V), fumarate (E₀=+0.03 V) or sulphur (E₀=-0.27 V) with formate as the electron donor. Bacteria growing in the presence of nitrate and fumarate were found to reduce both acceptors simultaneously, while the reduction of both nitrate and fumarate is blocked during growth with sulphur. These observations were paralleled by the presence and absence of the corresponding bacterial reductase activities. Using a specific antiserum, fumarate reductase was shown to be present in bacteria grown with fumarate and nitrate, and to be nearly absent from bacteria grown in the presence of sulphur. The contents of polysulphide reductase, too, corresponded to the enzyme activities found in the bacteria. This suggests that the activities of anaerobic respiration are regulated at the biosynthetic level in W. succinogenes. Thus nitrate and fumarate reduction are repressed by the most electronegative acceptor of anacrobic respiration, sulphur. By contrast, in Escherichia coli a similar effect is exerted by the most electropositive acceptor, O₂. W. succinogenes also differs from E. coli in that fumarate reductase is not repressed by nitrate.Abbreviations BV benzyl viologen - DMN 2,3-dimethyl-1,4-naphthoquinone - DMSO dimethylsulfoxide - TMAO trimethylamine-N-oxide     

Reconstitution of electron transport by cytochrome c-553 in a cell-free system of Nostoc muscorum

Treatment of spheroplasts of Nostoc museorum with hypotonic buffer results in membranes depleted of cytochrome c-553, but still active in photosynthetic and respiratory electron transport. These membranes retain full photosystem II activity (H₂ODAD_ox). Complete linear electron transport (H₂ONADP⁺), however, is decreased as compared with untreated spheroplasts. Addition of basic Nostoc cytochrome c-553 to depleted membranes reconstitutes NADP⁺ reduction and redox reactions of the photosystem I region as well.Using NADPH as electron donor, respiration of depleted membranes is also stimulated by adding cytochrome c-553, indicative of its function in respiratory electron transport.Cytochrome c-553 from Bumilleriopsis filiformis, Spirulina platensis (acidic types), Phormidium foveolarum (basic type), and mitochondrial horse-heart cytochrome c-550 are not effective in reconstituting both photosynthetic and respiratory electron transport, which points to a specific role of Nostoc cytochrome c-553.Abbreviations BSA bovine serum albumin - DAD 3,6-diaminodurene - DAD_ox 3,6-diaminodurene oxidized by potassium ferricyanide - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCIP 2,6-dichlorophenolindophenol - DPC 1,5-diphenylcarbazide - Fd ferredoxin - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - MES 2(-N-morpholino)-ethanesulfonic acid - MV methylviologen (1,1-dimethyl-4,4-bipyridylium dichloride) - PS I photosystem I - PS II photosystem II - Tris tris-(hydroxymethyl)-aminomethane     

Characterization and solubilization of residual redox activity in salt-washed and detergent-treated plasma membrane vesicles from spinach leaves

Summary An NADH-hexacyanoferrate(III) oxidoreductase (N-HCF-OR) was purified from spinach leaf plasma membrane (PM) vesicles; detailed biochemical analyses, however, revealed that the purifed protein is an NADH-monodehydroascorbate oxidoreductase (N-MDA-OR) located on the cytoplasmic surface of the PM. After removing all N-MDA-OR activity from the PM vesicles by consecutive treatments with hypoosmotic shock, salt, and detergents, the remaining PM (the stripped PM, SPM) fraction contained about 50% of the protein and 15% of the N-HCF-OR activity of the original PM fraction. The highest redox activity (100%) of the SPM fraction was obtained with NADH as electron donor and hexacyanofer-rate(III) (HCF) as electron acceptor, although redox activity could be measured also with ubiquinone-0 (23%), dichlorophenolindophenol (16%), cytochromec (9%), and Fe³⁺-EDTA (2%) as electron acceptors. The followingK _m values were obtained for the N-HCF-OR activity of SPM:K _m(NADH)=66.5 ± 3.8 M [with 200 M HCF(III)],K _m[HCF(III)]=11.1 ± 1.1 M (with 150 M NADH). NAD⁺ competitively inhibited the activity. Under special conditions, SB-16 (palmityl sulfobetaine, a zwitterionic detergent with a C-16 hydrocarbon chain) solubilized about 50% of the protein and more than 90% of the N-HCF-OR activity of the SPM fraction. Redox activity of the solubilized fraction with dichlorophenolindophenol as electron acceptor was 45% of that with HCF(III). The SB-16-solubilized fraction containedb-type cytochrome(s) which could be reduced by dithionite> ascorbate > NADH. Silver-stained sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the SB-16-solubilized SPM fraction revealed numerous polypeptides between 17 and 95 kDa. Further purification steps are needed to match the redox activities and spectrophotometric data to one or more of the polypeptides seen on the gel.Abbreviations c.m.c. critical micellar concentration - DCPIP 2,6-dichlorophenolindophenol - HCF(III) hexacyanoferrate(III) - MDA monodehydroascorbate - N-DCPIP-OR NADH-2,6-dichlorophenol-indophenol oxidoreductase - N-HCF-OR NADH-hexacyanoferrate(III) oxidoreductase - N-MDA-OR NADH-monodehydro-ascorbate oxidoreductase - PM plasma membrane - SB-16 N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (palmityl sulfobetaine, a zwitterionic detergent with a C-16 hydrocarbon chain) - SPM stripped plasma membrane     

Effects of electron donors and acceptors on anaerobic reduction of azo dyes by <Emphasis Type="Italic">Shewanella decolorationis</Emphasis> S12

Shewanella decolorationis S12 was able to reduce various azo dyes in a defined medium with formate, lactate, and pyruvate or H₂ as electron donors under anaerobic conditions. Purified membranous, periplasmic, and cytoplasmic fractions from strain S12 analyzed, respectively, only membranous fraction was capable of reducing azo dye in the presence of electron donor, indicating that the enzyme system for anaerobic azoreduction was located on cellular membrane. Respiratory inhibitor Cu²⁺, dicumarol, stigmatellin, and metyrapone inhibited anaerobic azoreduction by purified membrane fraction, suggesting that the bacterial anaerobic azoreduction by strain S12 was a biochemical process that oxidizes the electron donors and transfers the electrons to the acceptors through a multicompound system related to electron transport chain. Dehydrogenases, cytochromes, and menaquinones were essential electron transport components for the azoreduction. The electron transport process for azoreduction was almost fully inhibited by O₂, 6 mM of , and 0.9 mM of , but not by 10 mM of Fe³⁺. The inhibition may be a result from the competition for electrons from electron donors. These findings impact on the understanding of the mechanism of bacterial anaerobic azoreduction and have implication for improving treatment methods of wastewater contaminated by azo dyes.     

Estimation ofEscherichia coli mortality in seawater by the decrease in3H-label and electron transport system activity

The mortality ofEscherichia coli in seawater was assessed by viable counts, electron transport system activity, and cellular³H-labelling. Filtration was used to assess the grazing mortality. Cellular radiolabelling and electron transport system activity were useful methods for assessingE. coli survival in seawater. The decrease in the³H-label as a method to assess bacterial mortality was validated by using viable counts and metabolic activity assays. The particulate fraction that passed 2 m but was retained on 0.2 m pore-size filters was the primary reason forE. coli mortality in seawater.     

Rates of vectorial proton transport supported by cyclic electron flow during oxygen reduction by illuminated intact chloroplasts

The light-dependent quenching of 9-aminoacridine fluorescence was used to monitor the state of the transthylakoid proton gradient in illuminated intact chloroplasts in the presence or absence of external electron acceptors. The absence of appreciable light-dependent fluorescence quenching under anaerobic conditions indicated inhibition of coupled electron transport in the absence of external electron acceptors. Oxygen relieved this inhibition. However, when DCMU inhibited excessive reduction of the plastoquinone pool in the absence of oxygen, coupled cyclic electron transport supported the formation of a transthylakoid proton gradient even under anaerobiosis. This proton gradient collapsed in the presence of oxygen. Under aerobic conditions, and when KCN inhibited ribulose bisphosphate carboxylase and ascorbate peroxidase, fluorescence quenching indicated the formation of a transthylakoid proton gradient which was larger with oxygen in the Mehler reaction as electron acceptor than with methylviologen at similar rates of linear electron transport. Apparently, cyclic electron transport occured simultaneously with linear electron transport, when oxygen was available as electron acceptor, but not when methylviologen accepted electrons from Photosystem I. The ratio of cyclic to linear electron transport could be increased by low concentrations of DCMU. This shows that even under aerobic conditions cyclic electron transport is limited in isolated intact chloroplasts by excessive reduction of electron carriers. In fact, P₇₀₀ in the reaction center of Photosystem I remained reduced in illuminated isolated chloroplasts under conditions which resulted in extensive oxidation of P₇₀₀ in leaves. This shows that regulation of Photosystem II activity is less effective in isolated chloroplasts than in leaves. Assuming that a Q-cycle supports a H⁺/e ratio of 3 during slow linear electron transport, vectorial proton transport coupled to Photosystem I-dependent cyclic electron flow could be calculated. The highest calculated rate of Photosystem I-dependent proton transport, which was not yet light-saturated, was 330 mol protons (mg chlorophyll h)^–1 in intact chloroplasts. If H⁺/e is not three but two proton transfer is not 330 but 220 mol (mg Chl H)^–1. Differences in the regulation of cyclic electron transport in isolated chloroplasts and in leaves are discussed.     

The role of phospholipids in regulating photosynthetic electron transport activities: Treatment of thylakoids with phospholipase C

The involvement of phospholipids in the regulation of photosynthetic electron transport activities was studied by incubating isolated pea thylakoids with phospholipase C to remove the head-group of phospholipid molecules. The treatment was effective in eliminating 40–50% of chloroplast phospholipids and resulted in a drastic decrease of photosynthetic electron transport. Measurements of whole electron transport (H₂Omethylviologen) and Photosystem II activity (H₂Op-benzoquinone) demonstrated that the decrease of electron flow was due to the inactivation of Photosystem II centers. The variable part of fluorescence induction measured in the absence of electron acceptor was decreased by the progress of phospholipase C hydrolysis and part of the signal could be restored on addition of 3-(3,4-dicholorophenyl)-1,1-dimethylurea. The B and Q bands of thermoluminescence corresponding to S₂S₃Q_B ^– and S₂S₃Q_A ^– charge recombination, respectively, was also decreased with a concomitant increase of the C band, which originated from the tyrosine D⁺Q_A ^– charge recombination. These results suggest that phospholipid molecules play an important role in maintaining the membrane organization and thus maintaining the electron transport activity of Photosystem II complexes.Abbreviations DCMU 3-(3,4-dicholorophenyl)-1,1-dimethylurea - F_var variable fluorescence - LHC light-harvesting complex - MGDG monogalactosyldiacylglycerol - PS photosystem     

Uptake of sulfate,sulfite and thiosulfate by proton-anion symport in Desulfovibrio desulfuricans

pH changes and sulfide production upon addition of sulfate, sulfite or thiosulfate to non-buffered H₂-saturated cell suspensions of Desulfovibrio desulfuricans were studied by means of electrodes. The addition of these electron acceptors resulted in a rapid alkalinization of the suspension which was accompanied by sulfide production. At-2° C, alkalinization without immediate sulfide production could be obtained. After addition of ³⁵S-labelled sulfate at-2° C, the label was found to be concentrated 7,500-fold in the cells, while 2 protons per sulfate molecule had disappeared from the outer bulk phase. Alkalinization and sulfide production from micromolar electron acceptor additions depended on the transmembraneous proton gradient ( pH), and were reversibly inhibited in alkaline solution (pH>8.0) or by the protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP). Protonophore-inhibited sulfide production from sulfite or thiosulfate could be restored if the cell membranes were permeabilized by the detergent cetyltrimethylammonium bromide (CTAB), or if downhill transport was made possible by the addition of electron acceptors at millimolar concentrations. Sulfate was not reduced under these conditions, presumably because the cells did not contain ATP for its activation. K⁺-and Na⁺-ionophores such as nigericin, valinomycin or monensin appeared to be of limited efficiency in D. desulfuricans. In most experiments, sulfate reduction was inhibited by the K⁺–H⁺ antiporter nigericin in the presence of K⁺, but not by the thiocyanate anion or the K⁺-transporter valinomycin. The results indicate that sulfate, sulfite and thiosulfate are taken up by proton-anion symport, presumably as undissociated acids with an electroneutral mechanism, driven by the transmembraneous pH gradient ( pH) or by a solute gradient. Kinetics of alkalinization and sulfide production in cells grown with different electron acceptors revealed that D. desulfuricans has different specific uptake systems for sulfate and thiosulfate, and obviously also for sulfite. It is proposed that the electron acceptor transport finally will not consume net energy during growth in buffered medium: The protons taken up during active electron acceptor transport leave the cell with the reduced end-product by simple passive diffusion of H₂S.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone - FCCP carbonyl cyanide p-trifluoromethoxy phenylhydrazone - CTAB cethyltrimethylammonium bromide     

Evidence for two types of electron transfer processes through Photosystem II

Inhibition of electron flow from H₂O to methylviologen by 3-(34 dichlorophenyl)-1,1 dimethyl urea (DCMU), yields a biphasic curve — an initial high sensitivity phase and a subsequent low sensitivity phase. The two phases of electron flow have a different pH dependence and differ in the light intensity required for saturation.Preincubation of chloroplasts with ferricyanide causes an inhibition of the high sensitivity phase, but has no effect on the low sensitivity phase. The extent of inhibition increases as the redox potential during preincubation becomes more positive. Tris-treatment, contrary to preincubation with ferricyanide, affects, to a much greater extent, the low sensitivity phase.Trypsin digestion of chloroplasts is known to block electron flow between Q _A and Q _B, allowing electron flow to ferricyanide, in a DCMU insensitive reaction. We have found that in trypsinated chloroplasts, electron flow becomes progressively inhibited by DCMU with increase in pH, and that DCMU acts as a competitive inhibitor with respect to [H⁺]. The sensitivity to DCMU rises when a more negative redox potential is maintained during trypsin treatment. Under these conditions, only the high sensitivity, but not the low sensitivity phase is inhibited by DCMU.The above results indicate the existence of two types of electron transport chains. One type, in which electron flow is more sensitive to DCMU contains, presumably Fe in a Q _A Fe complex and is affected by its oxidation state, i.e., when Fe is reduced, it allows electron flow to Q _B in a DCMU sensitive step; and a second type, in which electron transport is less sensitive to DCMU, where Fe is either absent or, if present in its oxidized state, is inaccessible to reducing agents.Abbreviations DCMU 3-(34 dichlorophenyl)-1, 1 Dimethyl urea - MV methyl viologen - PS II Photosystem II - Tris tris (hydroxymethyl)aminomethane     

Development of photosynthetic electron transport reactions under the influence of phytohormones and nitrate nutrition in greening cucumber cotyledons

Development of the photosynthetic electron transport system, under the influence of hormones and nitrate-nutrition, in greening cucumber cotyledon was investigated. Both photosystems, PS I measured as DCPIP MV, and PS II as H₂O pBQ, were significantly promoted by GA and kinetin with kinetin being more effective. PS II/PS I ratio, though increased in control, did not change significantly with GA or kinetin treatment. Other partial reactions (H₂O MV/K₃Fe(CN)₆/NADP) were also promoted. Addition of KNO₃ showed concentration-dependent effects on growth and photosynthetic electron transport reactions (H₂O MV/K₃Fe(CN)₆/NADP). It is concluded that both hormones and nutritional status influence development of the photosynthetic electron transport system in greening cucumber cotyledons.Abbreviations PS I Photosystem I - PS II Photosystem II - BSA Bovine Serum Albumin - DCMU 3-(3,4-Dichlorophenyl)-1,1-Dimethyl Urea - DCPIP 2,6-Dichlorophenol Indophenol - EDTA Ethylene Diamine Tetra-acetic Acid - GA Gibberellic acid (GA₃) - HEPES (N-2-Hydroxyethyl Piperazine-N-2-Ethanesulphonic Acid) - IAA Indole-3-acetic acid - MV Methyl Viologen - NADP Nicotinamide Adenine Dinucleotide Phosphate - pBQ p-benzoquinone     

Heterogeneous photosystem 2 activity in isolated spinach chloroplasts

A study was made of the fluorescence induction curves from gently-broken spinach chloroplasts inhibited with DCMU. It was found that there were four kinetically different phases associated with such curves of which only the fastest did not appear to follow exponential kinetics. A comparison of the effects of various concentrations of DCMU on the rate of oxygen evolution and on the fluorescence induction curve did not support the hypothesis that any of the kinetic phases was simply an artefact caused by incomplete inhibition of electron transport. It was also found that 5 min of dark incubation did not maximally oxidize the electron acceptors to photosystem 2 since some acceptors were only oxidized following far-red illumination, suggesting a heterogeneity among these acceptors with respect to their re-oxidation properties. Investigation of the effect of the Q₄₀₀ oxidation state on the fluorescence induction curve revealed that it only influenced the slowest kinetic phase and that Q₄₀₀ did not seem to be associated with the other phases.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1 - 1 dimethylurea - PS 1 photosystem 1 - PS2 photosystem 2 - HEPES N-2-Hydroxyethylpiperazine-N-2-ethanesulfonic acid - EDTA ethylene-diaminetetraacetic acid - F_max maximum yield of fluorescence emission - F₀ initial yield of fluorescence emission - F_v variable yield of fluorescence emission - N.E. non-exponential kinetics