Hydrogen Ion Uptake Research Articles

Two types of ammonium uncoupling in pea chloroplasts.

The effect of ammonium on ATP synthesis, electron transfer, and light-induced uptake of hydrogen ions in pea chloroplasts was studied. It is shown that the dependence of these reactions on ammonium concentration could be due to effects of two different uncoupling processes. The first process is induced by low ammonium concentrations (<0.2 mM); the second one is observed in the NH(4)Cl concentration interval of 0.5-5.0 mM. The first type of uncoupling is stimulated by palmitic acid or by N,N'-dicyclohexylcarbodiimide, while the second is stimulated by chloroplast thylakoid swelling caused by energy-dependent osmotic gradients. In the presence of the fluorescent dye sulforhodamine B, which does not penetrate through the cell membrane, this swelling causes the dye to enter the lumens. It is supposed that ammonium activates two different routes of cation leakage from the lumen. The first route involves channel proteins, while the second is a mechanosensitive pore that opens in response to osmotic gradients.

Synergism of ammonium and palmitic acid in uncoupling of electron transfer and ATP synthesis in chloroplasts.

Uncoupling by ammonium of electron transfer and ATP synthesis during linear transfer of electrons from water to photosystem 1 acceptors was studied in pea chloroplasts. It was shown that 40 microM palmitic acid decreased several-fold the ammonium concentrations necessary for 50% inhibition of ATP synthesis. The protonophore carbonyl cyanide m-chlorophenylhydrazone has no such property. The enhancement by palmitate of ammonium-induced uncoupling is accompanied by acceleration of basal electron transfer and decrease in the photoinduced uptake of hydrogen ions (H+). In the absence of ammonium, palmitate has no effect on basal transport and stimulates uptake of hydrogen ions. This means that in the case of combined action of palmitate and ammonium an additional leakage of H+ takes place, resulting in dissipation of the pH gradient. Synergic action of two metabolites, free fatty acid and ammonium, is supposed to provide for functioning of a system of mild regulation of energy coupling processes in native plant cell chloroplasts. Possible mechanisms of synergism are discussed.

Decationization and dealumination of clinoptilolite tuff and ammonium exchange on acid-modified tuff

The paper presents results of investigation of exchange of the clinoptilolite tuff cations with hydrogen ions from HCl solution of concentration 0.1 mmol cm −3 and ammonium ions solutions of concentrations 0.0071 to 2.6 mmol cm −3. Molal concentrations, x (mmol g −1) of cations exchanged in acid solution and in ammonium ions solutions were compared with molal concentrations of cations obtained by determination of the cation-exchange capacity of clinoptilolite tuff. The obtained results show that at ammonium ion concentrations lower than 0.1 mmol cm −3, with regard to exchange capacity for particular ions, best exchanged are Na + ions, followed by Mg 2+ and Ca 2+ ions, while exchange of K + ions is the poorest (Na + > Mg 2+ > Ca 2+ > K +). At ammonium concentrations from 0.2 to 1 mmol cm −3 the order is Na + > Ca 2+ > Mg 2+> K +. At concentrations higher than 1 mmol cm −3 the order is Na + > Ca 2+ > K + > Mg 2+. The results are a consequence of the uptake of hydrogen ions by zeolite samples in ammonium ions solutions at concentrations lower than 1 mmol cm −3 and indicate the importance of Mg 2+ (besides Na + ions) for the exchange between clinoptilolite cations and H + ions, in contrast to K + ions, whose participation in the reaction with H + ions is the lowest. During decationization of the clinoptilolite in acid solution, best exchanged are Na +, Mg 2+, and Ca 2+ ions, while exchange of K + ions is the poorest. Due to poor exchange of K + and H + ions and good exchange of Na +, Mg 2+, and Ca 2+ ions, it is to be assumed that preservation of stability of the clinoptilolite structure is caused by K + ions present in the channel C. Clinoptilolite is dissolved in the clinoptilolite A and B channels where Na +, Mg 2+, and Ca 2+ ions are present. On the acid-modified clinoptilolite samples, exchange of ammonium ions is poorer than on natural zeolite. The longer the contact time of the zeolite and acid solution, the worse ammonium ions exchange. It can be assumed that H + ions exchanged with zeolite cations are consumed for solution of aluminum in the clinoptilolite structure; therefore the concentration of H + ions as exchangeable cations decreases. In the ammonium ion solution at a concentration of 0.0065 mmol cm −3, from the acid-modified zeolite samples, Al 3+ ions are exchanged best, followed by Na +, Mg 2+, Ca 2+, and K + ions. Further to the results, it is to be assumed that exchangeable Al 3+ ions available from clinoptilolite dissolution are best exchanged with H + ions in acid solution.

Formation of α-ω(4,7,10,13-pentaoxa-16-azacyclooctadecane) hexadecane micelles in aqueous solution – effect of HCl addition

The structure of aggregates of a new bolaform surfactant [α-ω (4,7,10,13-pentaoxa-16-azacyclooctadecane) hexadecane] in neat aqueous solution has been investigated by small-angle neutron scattering. Preliminary data analysis unequivocally indicates that globular micelles are formed. This finding has been confirmed by the analysis of data obtained upon addition of hydrochloric acid. The observed significant reduction of micelle aggregation number has been attributed to the peculiar complexing ability of the two aza-crown ether units in the surfactant molecule; this is in line with information inferred from the complexation of ions into the non alkylated azacrown ethers. As a consequence of hydrogen ion uptake into the aza-crown ether unit, the partial ionization of surfactant causes a decrease in the micelle dimension that follows the increased repulsion among head groups.

Voltammetric studies of electrochemical pretreatment of rotating-disc glassy carbon electrodes in phosphate buffer

Cyclic voltammetry was used to study the formation of graphite oxide film on the surface of rotating-disc glassy carbon electrodes. The film was formed by continuous potential cycling in phosphate buffer electrolyte. It was found that when cycling between the totally oxidized and totally reduced potential ranges (between + 2.3 and −1.2V vs. SCE), well-shaped redox peaks were obtained. Typical voltammograms comprised one cathodic and two anodic waves, where the anodic waves were directly related to the oxidation of surface-bound products associated with the cathodic process. All three processes were pH dependent. Freshly formed surface graphite oxide films were not stable and would undergo transformation to give the stable state upon potential cycling between potentials ± 1.0V. The ultimate stable voltammograms were characterized by two electrode processes. The quasi-reversible process involved surface quinone-like functional groups, while the other irreversible process might be related to the uptake and release of hydrogen ions at the porous graphite oxide film.

Chemistry of rainfall, throughfall and stemflow in a eucalypt forest and a pine plantation in south-eastern Australia: 2. Throughfall

A rainfall event-based study allowed the examination of factors affecting the amounts and chemical concentrations of throughfall. The amount and frequency of antecedent rainfall was of influence in both forests, in that concentrations were higher with dry antecedent conditions. The debarking season influenced throughfall in the eucalypt forest. Potassium was the dominant cation in the throughfall of both forests, being 50% of the sum of the major cations (Ca, Mg, Na and K) for the pines and 70% for the eucalypts. The largest difference was in sodium, being 29% of the combined cations for the pines and 10% for the eucalypts. There was net uptake of hydrogen ions from rainfall for both forests, i.e. throughfall was less acid than rainfall, but release occurred for a significant proportion of events and was associated with higher rainfall pH. There was a small net input of NH4-N and NO3-N by the eucalypts. A more substantial input of both ions occurred in the pines. However, uptake and release of both ions occurred for different events in both forests. Throughfall samples taken during events showed that the chemical concentration was related to variations in the intensity and continuity of the rainfall, particularly for the major cations. NH4-N and NO3-N did not always follow the cation trends through time.

Thorium and uranium uptake by natural zeolitic materials

The thorium and uranium uptake from their aqueous solutions by unpretreated and NaCl-pretreated zeolite-bearing volcanoclastic rock samples from Metaxades (Thrace, Greece) has been studied using a batch-type method. The concentration of the solutions varied between 50 and 20 000 mg/l. The NaCl pretreatment of the materials improved the thorium but not the uranium uptake. The absolute thorium uptake by the pretreated material, determined using neutron activation and X-ray fluorescence techniques, reached 12.41 mg/g, whereas the uranium uptake by the raw material was 8.70 mg/g. The uptake distribution coefficients ( K d) indicated that the relative thorium and uranium uptake is higher for initial concentrations below 250 mg/l. The zeolitic materials showed exceptional resistance to the initial low pH of the solutions used. The pH in was significantly increased due to the simultaneous hydrogen-ion uptake. The thorium and uranium uptake is a rather complicated phenomenon related to the aqueous chemistry of the elements, the nature of the constituent minerals and the properties of the zeoliferous rock specimens. The various metal species are bound through different uptake processes such as ion-exchange, adsorption and surface precipitation. Microporous minerals (zeolites, phyllosilicates) are mainly responsible for the considerable uptake ability of the rock samples studied.

Atmospheric Deposition and Foliar Leaching in a Regenerating Southern Appalachian Forest Canopy

SUMMARY (1) Incident precipitation, throughfall and stemflow were collected to examine the importance of factors potentially determining net canopy element fluxes, and to quantify canopy exchange and dry deposition rates in a regenerating southern Appalachian forest. (2) Net throughfall fluxes (throughfall minus precipitation transfers) showed consistent canopy effects on rainfall chemistry, with SO42~, PO43~, Cl~, K+, Ca2+ and Mg2+ added to rainfall by foliage, whereas NO3~-N, NH4+-N and H+ ions were absorbed from precipitation. Storm characteristics (event amount and duration) accounted for the largest portion of the variability in growing season net throughfall fluxes, suggesting that canopy exchange was the major mechanism of throughfall transfer. (3) Stemflow fluxes increased canopy exchange rates of SO42~, PO4?~, Cl~, K+, and Mg2+ by greater than 20% in a regression model of total below-canopy element fluxes. (4) Cation leaching fluxes were highly variable (C.V.>50%) over spatial scales of several m2, but could be explained largely by heterogeneity in canopy cover. (5) Foliar cation leaching losses in the early successional forest accounted for 4—13% of leaf nutrient reserves. As cation throughfall transfers were highest during storms with the greatest hydrogen ion uptake from rainwater, it is hypothesized that acid precipitation is causing accelerated foliar nutrient leaching in south-eastern hardwood forests.

Hydrochemistry, origin and evolution of sedimentary subsurface fluids: III. Early diagenetic mineralization reactions in high sedimentation—rate basins

The early diagenetic evolution of pore-water chemistry is closely linked to mineralization reactions which consume significant portions of the metabolites released by bacterial organic matter decomposition. These reactions are most intense in high-sedimentation rate basins and include the precipitation of iron-sulfides and various carbonates leading to concretion growth. Early diagenetic pyrite is typically framboidal attesting to its recrystallization from precursor mackinawite, greigite or amorphous FeS which are the favored phases at high supersaturation levels during the initial sulfate reduction stages. The sulfur isotopic composition of early diagnetic pyrite can be used to differentiate diffusion-controlled, open-system conditions with isotopically light sulfide (δ 34S = − 35 to − 20‰) from closed system conditions, under which Raleigh distillation produces increasingly heaver sulfide (δ 34 S = − 35 to + 18‰). Alabandite (Mn-sulfide) is a rare authigenic sulfide in Mn-rich environments such as certain restricted, semi-stagnant basins (Baltic Sea). pH-buffering by hydrogen sulfide and hydrogen ion uptake by the reduction of manganese and iron oxides and hydroxides in the nitrate and sulfate reduction zones raise the pH sufficiently to cause supersaturation of the porewaters with respect to Ca-, Mg-, Fe- and Mn-carbonates and complex solid solutions of them. Fe-carbonates cannot form in the sulfate reduction zone in the presence of dissolved sulfide which competes for the dissolved iron. Likewise, dolomite formation appears to be inhibited or slowed down in the presence of substantial dissolved sulfate. The appearance of siderite and ankerite therefore signals carbonate precipitation below the sulfate reduction zone. Supporting evidence for the early diagenetic origin of many carbonate concertions is provided by their high carbonate contents (70 to 90% reflecting the porosity existing at the time of precipitation, called “minus-cement porosity”), isotopic composition, clay fabrics, and preservation of original bedding features including the shapes of fossils and fecal pellets. In these environments increasing carbon isotope ratios (δ 13 C = − 20 to + 15‰) indicate concretion growth below the sulfate reduction zone, i.e., in the methane generation zones. Continuing concretion growth at greater burial depth explains pore water profiles with constantly low Ca and downward decreasing Mg concentrations. Dissolved ammonia and phosphate profiles reguire adsorption and ion-exchange reactions as additional removal machanisms (besides apatite precipitation) in order to explain their downward decrease after they have reached maximum concentrations below the alkalinity maximum. Classification of early diagnetic environments into oxic and anoxic and further subdivision of the latter into sulfidic and non-sulfidic (with suboxic or post-oxic and methanic as further subcategories of the non-sulfidic environment) according to Berner (1981) is preferred over the previous classification in terms of pH/Eh fields. The temperature range of the early diagenetic stage extends from O to about 75°C, at which temperature thermocatalytic organic matter decomposition replaces the earlier bacterially mediated reactions and causes a whole set of new diagenetic reactions (such as feldspar dissolution, smectite to illite transformation) to start.

Interaction of drugs with a model membrane protein: Effects of local anesthetics on electron transfer and hydrogen ion uptake in ionophore stimulated cytochrome oxidase proteoliposomes

Cytochrome oxidase extracted from beef heart was incorporated into vesicles composed of soy bean phospholipids (asolectin). The oxidation of externally added cytochrome c by such vesicles is associated with proton uptake from the external medium. The rates of both cytochrome c oxidation and proton uptake were stimulated by addition of ionophores such as trifluoromethoxy carbonyl cyanide phenylhydrazone (FCCP), nigericin and valinomycin. These agents probably dissipate pH and/or electrical potential gradients which develop as a result of enzyme activity and which have a “restraining” influence on the turnover of the oxidase. Local anesthetics inhibited oxidase activity but had a much greater effect on the stimulated (ionophore-treated) than the unstimulated enzyme. In addition, pretreating proteoliposomes with local anesthetics completely prevented the stimulating effects of these ionophores. Based on this and previous studies, a model was developed in which local anesthetics interacted with the phospholipid component of the oxidase complex resulting in reduced internal electron transfer and dissociation of the oxidase from the regulatory role of the proton gradient.

Measurement of glucose in plasma by a differential pH technique.

A new automatic apparatus based on the differential measurement of pH between two solutions has been developed. Two 25-microL (internal volume) glass capillary electrodes are used to measure the results of automated (under microcomputer control) chemical reactions that lead to the liberation or the uptake of hydrogen ions. The sensitivity of the differential pH measurements is better than +/- 0.0001 pH unit, and the change in H+ concentration that can be detected by such an apparatus is 1 mumol/L for plasma and 3 mumol/L for whole blood. The technique has been applied to the measurement of glucose in plasma, giving results in agreement with the specifications of the Food and Drug Administration reference method for quantitative determination of glucose (hexokinase/glucose-6-phosphate dehydrogenase method).

Respiratory properties of blood of the gray seal,Halichoerus grypus

1. This study examined the O2 and CO2 transport and acid-base properties of blood of the gray seal. Phocid seals use theblood as an oxygen store for aerobic metabolism during diving. Particular objectives were to determine whether CO2 exerts a specific effect on blood oxygen affinity, and whether the Bohr coefficient varies between different levels of oxygen saturation. 2. Hematocrit (0.50), blood hemoglobin concentration (12.8 mM heme) and cell hemoglobin concentration (25.4 mM) were, high compared to terrestrial mammals but similar to other seals (Table 2). Isoelectric focusing resolved the same four hemoglobin components in six individuals, with the most important components constituting 60% and 20% of the total. Oxygen affinity (P50=27.1 Torr at pH 7.4, 37.5°C) and equilibrium curve shape (nH=2.59) were similar to other phocid seals and terrestrial mammals (Tables 1,4). The Bohr coefficient for CO2 induced pH change (−0.51) was only slightly higher than that for fixed acid incuded pH change (−0.47), implying little oxygen-linked carbamino formation (Table 1). The bohr coefficients were at the upper end of the range found in terrestrial mammals, and did not vary with oxygen saturation (Table 1). 3. Blood buffer value was high (31.5 mM/pH), in accord with the high hemoglobin concentration (Table 3). The Haldane effect (−0.32 mol CO2 per mol O2, Fig. 2) was similar to those in blood of other seals and dog, but higher than that in human blood. Hydrogen ion uptake by hemoglobin upon deoxygenation (0.40 mol/mol O2) was greater than in human blood, in proportion to the larger fixed acid Bohr coefficient in the seal. 4. Blood of the gray seal, like that of other phocid seals, is distinguished from that of terrestrial mammals primarily by high hemoglobin concentration and oxygen capacity, which increase blood oxygen stores available for use during diving. Other properties are similar to those of terrestrial mammals or differ only as a consequence of the high hemoglobin concentration.

The Effect of Heavy Metal Compounds on the Permeability of Chlorella Cells

The loss of potassium from Chlorella is investigated when cells are exposed to 12 heavy metal compounds including zinc chloride (ZnCl 2) , mercuric chloride (HgCl 2 ), cupric chloride (CUCl 2 ), methylmercuric chloride (MeHg) and phenylmercuric acetate (PhHg). Over 90% of the potassium loss occurs under both dark or light conditions; the rest appears to require energy from photosynthesis. The effects of C0 2 -free air, anaerobic conditions and the photosynthetic inhibitor 3-(3'-4'-dichlorophenyl)-1,1-dimethylurea (DCMU) are investigated. In the light, potassium loss (efflux) is not coupled to a hydrogen ion (H + ) uptake mechanism during net ion movement. The effects of zinc and mercury ions on potassium loss at sublethal concentrations appeared to be minimal, and toxicity as well as resistance cannot be explained by gross changes in internal potassium levels. The results suggest that only at high concentrations, the primary effect caused by heavy metal ions is to increase the permeability of cells. The metal induced loss of potassium is strongly correlated to the strength of the metal-sulphydryl (-SH) bond, and the implications of this in relation to permeability of cell walls and membranes are discussed.

Hydrogen ion uptake upon tobacco mosaic virus protein polymerization

To determine the stage at which H + ions are bound during the entropy-driven polymerization of tobacco mosaic virus protein, acid-base titrations were carried out at a concentration of 5 mg/ml in 0.1 m-KCl from pH 8 to pH 5.2 and back to pH 8 at 4, 10, 15 and 20 °C. The titration was always completely reversible when the addition of acid or base was so slow that the experiment required seven hours in each direction. When the titration was started at pH 7 and performed down and up twice as rapidly, a hysteresis loop, indistinguishable from one previously published, was obtained at 20 °C. Ultracentrifugation experiments were carried out at selected pH values at the four temperatures. H + ion uptake, as determined from the reversible titration curves, is correlated with the disappearance of the 4 S component and is independent of whether the polymerized species is in a 20 S or higher state of aggregation. At pH 7, approximately 1 mole of H + ion is bound per mole of monomer. At pH values between 6.56 and 6.05, 1.5 moles of H + ion are bound per mole of monomer upon polymerization. At pH 6.05, 0.5 mole of H + ion is bound before any polymerization takes place. Tobacco mosaic virus protein at 20 °C in an unbuffered 0.1 m-KCl solution at pH 7.18 at a concentration of 41 mg/ml, largely in the 20 S state, was depolymerized entirely to the 4 S state by dilution with 0.1 m-KCl adjusted to the same pH. Under these conditions, there was no pH change, indicating that no H + ions are released. These seemingly contradictory findings can be explained by assuming that the 4 S component polymerizes to form either double discs without binding H + ions, or, alternatively, two-turn helices accompanied by the binding of H + ions. Both double discs and two-turn helices sediment at approximately 20 S. Whether polymerization in the neighborhood of pH 7 leads to helices or discs depends upon the availability of H + ions.

Topotactic redox reactions and ion exchange of layered MoO 3 bronzes

Chemical or electrochemical reduction of MoO 3 in neutral aqueous electrolyte solutions results in the reversible topotactic formation of a new type of molybdenum oxide bronzes A + x(H 2O) y[MoO 3] x−. The latter are built up by negatively charged [MoO 3] x− layers with exchangeable hydrated cations in the interlayer space. Non-solvated cations are taken up between the MoO 3 sheets on cathodic reduction of the oxide in organic electrolyte solutions. Galvanostatic studies on the reduction of MoO 3 in aqueous acids reveal the strong influence of kinetics on hydrogen ion uptake. Earlier results of Glemser (2) on “genotypic” hydrogen bronzes of MoO 3 are confirmed. H 0.5MoO 3 was found to exhibit Brönsted acid character and to form a novel type of layer intercalation compounds L xH 0.5MoO 3 with Lewis bases.

Alkaline Isomerization of Oxidized Cytochrome c: EQUILIBRIUM AND KINETIC MEASUREMENTS

Equilibrium and kinetic studies of the isomerization of horse heart ferricytochrome c at alkaline pH have been carried out using difference spectroscopy and stopped flow techniques. The minimal reaction scheme is: [see PDF for equation] where CH and C are species of ferricytochrome c which exhibit a 695 nm absorbance band, and NC (no color) is a form without this band; the oxidation-reduction potentials of CH and NC differ significantly. The values of the constants in this scheme were determined at 25° except for the oxidation and reduction rate constants, which were determined at 22°. The pH dependence of the observed rate constant for the conformational changes was measured as the change in the 695 nm band absorbance and as the release and uptake of hydrogen ions. From this it was calculated that the ionizing group in the scheme above has an apparent pK of 11.0 ± 0.1 at 25°. The conformation equilibrium constant, Kc, defined as κf/κb, was found to be 125 ± 36 at 25°. An over-all pK of 9.0 was calculated from the product of the equilibrium constants, in agreement with the over-all pK of 9.0 determined from the pH dependence of the 695 nm band at equilibrium. Spectrophotometric measurements at 243 nm indicate that tyrosine is not the ionizing group with an apparent pK of 11. It is suggested that the difference in oxidation-reduction potential and the absorbance band at 695 nm arises by substituting the sulfur of Met-80 as one of the ligands of the iron porphyrin in CH by the e-amino group of Lys-79 in NC. This suggestion, consistent with structural information, is accessible to experimental verification.

Light-dependent Inhibition of Photophosphorylation by N-Ethylmaleimide

Abstract The treatment of chloroplasts with 1 mm N-ethylmaleimide (NEM) in the light, but not in the dark, resulted in a partial, permanent inhibition of photophosphorylation. Noncyclic electron flow coupled to phosphorylation was also inhibited on incubation of chloroplasts with NEM in the light, but this inhibition was reversed by ammonium chloride. The uncouplers, carbonyl cyanide m-chlorophenylhydrazone and ammonium chloride, largely prevented the inhibition. Adenosine triphosphate and adenosine diphosphate partially protected phosphorylation from inhibition by light and NEM. Light-induced hydrogen ion uptake was unaffected by NEM except that the uptake stimulated by adenosine triphosphate was inhibited. The calcium-dependent adenosine triphosphatase of coupling factor 1 was also inhibited in chloroplasts treated with NEM in the light prior to extraction of the coupling factor. It is suggested that light causes a conformational change in the membrane-bound coupling factor, allowing the reaction of a group (or groups) with NEM. The sensitivity of the inhibition to adenine nucleotides suggests that these nucleotides modify the conformation of coupling factor 1 in the light.

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

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.

Effect of hydrocarbon chain length on the uncoupling of photophosphorylation by amines

The effectiveness of normal aliphatic amines in uncoupling photophosphorylation in chloroplasts increases dramatically with increasing number of carbon atoms. A similar effect was observed in subchloroplast particles, except that phosphorylation in these preparations was less sensitive to inhibition by aliphatic amines with less than five carbon atoms than phosphorylation in chloroplasts. A linear relationship between the log of the concentration of the amines required to give 50% inhibition of photophosphorylation and the log of their octanol/water partition coefficients was obtained for ethyl- through hexyl-amines. A similar relationship was found for hexylthrough nonyl-amines except that the inhibition increased more dramatically with increasing chain length than for the shorter chain amines. In contrast, the log of the activity of the amines in the inhibition of hydrogen ion uptake in chloroplasts was linearily related to the log of their octanol/water partition coefficients for all amines tested. The trypsin-activated, Ca 2+-dependent adenosine triphosphatase of purified coupling factor 1 from chloroplasts was insensitive to inhibition by short chain amines, but was strongly inhibited by long chain amines. The dependency of the inhibition of this reaction by amines on their hydrocarbon chain length was similar to that observed in the inhibition of phosphorylation. The inhibition of photophosphorylation by long chain amines may, therefore, be caused in part by their effects on coupling factor 1. Phosphorylation in subchloroplast particles supplemented with valinomycin is inhibited by ammonium chloride. In the presence of these reagents, phosphorylation in subchloroplast particles may be stimulated by amines. The effectiveness of amines in stimulating phosphorylation under these conditions paralleled their effectiveness as uncouplers. This observation provides evidence that this stimulatory action of the amines is related to their action as uncouplers.

Isolation and properties of a protein from chloroplasts required for phosphorylation and hydrogen ion uptake

Isolation and properties of a protein from chloroplasts required for phosphorylation and hydrogen ion uptake