The scientific legacy of Stuart Ferguson.

The effects of a photoinhibition treatment (PIT) on electron transport and photophosphorylation reactions were measured in chloroplasts isolated from triazine‐resistant and susceptible Chenopodium album plants grown under high and low irradiance. Electron transport dependent on photosystem I (PSI) alone was much less affected by PIT than that dependent on both photosystem II (PSII) and PSI. There was a smaller difference in susceptibility to PIT between the photophosphorylation activitity dependent on PSI alone and that dependent on both PSII and PSI. Because in all cases photophosphorylation activity decreased faster upon PIT than the rate of electron transport, we conclude that photoinhibition causes a gradual uncoupling of electron transport with phosphorylation. Since the extent of the light‐induced proton gradient across the thylakoid membrane decreased upon PIT, it is suggested that photoinhibiton causes a proton leakiness of the membrane. We have found no significant differences to PIT of the various reactions measured in chloroplasts isolated from triazine‐resistant and susceptible plants. We have also not observed any significant differences to PIT of the photophosphorylation reactions in chloroplasts of plants grown under low irradiance, compared with those grown under high irradiance. However, the electron transport reactions in chloroplasts from plants grown under low irradiance appeared to be somewhat less sensitive to PIT than those grown under high irradiance.

Photosynthetic electron transport and phosphorylation reactions in thylakoid membranes from the blue-green alga Anacystis nidulans

Photosynthetic electron transport reactions of succulent plants from hot deserts are able to tolerate extremely high temperatures and to acclimate to seasonal increases in temperature. In this study, we report the influence of relatively long, in vivo, high-temperature treatments on electron transport reactions for two desert succulents, Agave deserti and Opuntia ficus-indica, species which can tolerate 60 degrees C. Whole chain electron transport averaged 3 degrees C more sensitive to a 1-hour high-temperature treatment than did PSII (Photosystem II) which in turn averaged 3 degrees C more sensitive than did PSI. For plants maintained at day/night air temperatures of 30 degrees C/20 degrees C, treatment at 50 degrees C caused these reactions to be inhibited an average of 39% during the first hour, an additional 31% during the next 4 hours, and 100% by 12 hours. Upon shifting the plants from 30 degrees C/20 degrees C to 45 degrees C/35 degrees C, the high temperatures where activity was inhibited 50% increased 3 degrees C to 8 degrees C for the three electron transport reactions, the half-times for acclimation averaging 5 days for A. deserti and 4 days for O. ficus-indica. For the 45 degrees C/35 degrees C plants treated at 60 degrees C for 1 hour, PSI activity was reduced by 54% for A. deserti and 36% for O. ficus-indica. Acclimation leads to a toleration of very high temperatures without substantial disruption of electron transport for these desert succulents, facilitating their survival in hot deserts. Indeed, the electron transport reactions of these species tolerate longer periods at higher temperatures than any other vascular plant so far reported.

Freezing the effect of eutectic crystallization on biological membranes

Effects of 60Co γ radiation on thylakoid membrane functions in Anacystis nidulans

Various chloroplast proteins are activated/deactivated during the light/dark cycle via the redox regulation system. Although the photosynthetic electron transport chain provides reducing power to redox-sensitive proteins via the ferredoxin (Fd)/thioredoxin (Trx) pathway for their enzymatic activity control, how the redox states of individual proteins are linked to electron transport efficiency remains uncharacterized. Here we addressed this subject with a focus on the photosynthetic induction phase. We used Arabidopsis plants, in which the amount of Fd-Trx reductase (FTR), a core component in the Fd/Trx pathway, was genetically altered. Several chloroplast proteins showed different redox shift responses toward low- and high-light treatments. The light-dependent reduction of Calvin-Benson cycle enzymes fructose 1,6-bisphosphatase (FBPase) and sedoheptulose 1,7-bisphosphatase (SBPase) was partially impaired in the FTR-knockdown ftrb mutant. Simultaneous analyses of chlorophyll fluorescence and P700 absorbance change indicated that the induction of the electron transport reactions was delayed in the ftrb mutant. FTR overexpression also mildly affected the reduction patterns of FBPase and SBPase under high-light conditions, which were accompanied by the modification of electron transport properties. Accordingly, the redox states of FBPase and SBPase were linearly correlated with electron transport rates. In contrast, ATP synthase was highly reduced even when electron transport reactions were not fully induced. Furthermore, the redox response of proton gradient regulation 5-like photosynthetic phenotype1 (PGRL1; a protein involved in cyclic electron transport) did not correlate with electron transport rates. Our results provide insights into the working dynamics of the redox regulation system and their differential associations with photosynthetic electron transport efficiency.

It is now well known that the role of a universal chemical energy currency in living cells is played by the so-called high-energy compound adenosine triphosphate (ATP), whose endergonic synthesis from adenosine diphosphate (ADP) and inorganic phosphate (ΔG0’ = + 31 kJ mol-1) permits the cell to store free energy in a kinetically stable chemical form. One source of the free energy necessary to drive this reaction lies in processes such as oxidative metabolism or photosynthetic electron flow, and the overall process of ATP synthesis coupled to electron transfer is thus referred to as electron transport phosphorylation (see e.g. Stryer, 1981, Lehninger, 1982). The question then arises as to the nature of the free energy transfer between the (exergonic) reactions of electron transport and the otherwise endergonic synthesis of ATP. It is usual to encapsulate this question in the form of a scheme (equation 1) in which a ‘high energy intermediate’, often denoted “∼” (“squiggle”), constitutes the energetic link between electron transport and ATP synthesis; it is the nature of this “∼” that forms the subject of the present considerations.

The electron transport and back reaction in nanocrystalline TiO2 films prepared at low temperature using a new hydrothermal crystallization method on conductive glass and plastic substrates have been investigated by intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS). The hydrothermal method enables the preparation of crack-free TiO2 thick films and at the same time enhances the electron transport compared to films prepared by low-temperature sintering, providing a path towards efficient photoelectrode materials for flexible dye-sensitized solar cells. UV/ozone treatment of the films enables the removal of residual organics left from the hydrothermal preparation process. Since these organics represent surface states that mediate the back reaction of electrons, the electron lifetime is increased by their removal, while the electron transport is not enhanced significantly. High-temperature sintering of the hydrothermally prepared films leads to both a removal of the surface states and a significant enhancement of the electron transport properties. Interestingly, the electron lifetimes are not changed by high-temperature sintering, since faster electron transport and less surface states have opposite effects on the back reaction process. These films showed improved electron transport properties and efficiencies even if compared with films prepared by conventional high-temperature methods, which shows the high potential for the further development of the hydrothermal method.

Electron transport reactions between pyrene and methylviologen in a model biological membrane

Studies of the intracellular role of myoglobin were carried out by recording spectrophotometric changes in acid metmyoglobin and oxymyoglobin during electron transport reactions with mitochondria prepared from pigeon heart muscle by the method of Chance and Hagihara. The absorption peak of metmyoglobin at 409 mµ disappeared when substrate was added to normal or antimycin-inhibited preparations, and was replaced by a new maximum at 423 to 424 mµ, identified as due to the oxidation to ferrylmyoglobin. Further investigation revealed that the oxidation of metmyoglobin took place with the simultaneous oxidation of reduced flavoprotein. Hydrogen peroxide, formed by the reaction of reduced flavoprotein with oxygen, was considered to be the probable intermediate for the oxidation of metmyoglobin in experiments in which catalase was added as a competitor for the oxidant. When DPNH was added to the reaction mixture, the reductant acted to resynthesize the ferri-derivative by reaction with ferrylmyoglobin. Oxymyoglobin could not be used in place of metmyoglobin in these systems. Under the experimental conditions, oxymyoglobin dissociated when dissolved oxygen was depleted from the medium by enzyme oxidations; the resultant ferromyoglobin underwent oxidation to metmyoglobin.

Porcine reproductive and respiratory syndrome is an infectious disease that causes serious economic losses to the swine industry worldwide. To better understand the pathogenesis of the porcine reproductive and respiratory syndrome virus (PRRSV), three PRRSV strains with different molecular markers and virulence were used to infect MARC-145 cells. A total of 1804 proteins were identified, and 233 altered proteins and 72 signaling pathways involved in the proteomic profiling of virus-infected MARC-145 cells increased with the virulence of the PRRSV strain. The three types of viral strains shared a common pathway—the electron transport reaction in mitochondria—in the infected-MARC-145 cells. Moreover, the antisense pathway was the most variable of all significant signaling pathways for the highly virulent SX-1 strain, indicating that this unique pathway may be connected to the high virulence of the SX-1 strain. Our study is the first attempt to provide a proteome profile of MARC-145 cells infected with PRRSV strains with different virulence, and these findings will facilitate a deep understanding of the interactions between this virus and its host.

Paraquat (PQ) is a nonselective bipyridyl herbicide widely used in agriculture to control weeds, but its accidental, occupational, or intentional exposure in humans is known to cause pneumo- and neurotoxicity which may proves fatal. Oxidative stress is reported as an underlined mechanism of PQ-induced toxicity in alveolar cells, neurons, and astroglia. PQ generates superoxides both through electron transport reaction (ETC) with nicotinamide adenine dinucleotide-dependent oxidoreductase and by the redox cycling via reaction with molecular oxygen. In lungs, it causes edema and inflammation resulting in neutrophils infiltration and subsequent activation of pro-inflammatory cytokines. In the present study, toxicity of subacute oral PQ exposure and effect of resveratrol (Res) and/or tetracycline (TC) on oxidative stress and inflammatory markers in lungs, brain, and liver was studied. Levels of glutathione and malondialdehyde and activities of myeloperoxidase, glutathione peroxidase, and catalase were measured in lungs, brain, and liver. PQ interferes in the function of mitochondrial ETC complexes causing decreased adenosine triphosphate levels, and hence the activities of complexes I and IV were studied in brain tissues. Res, a natural antioxidant, and TC, an antibiotic with its antimicrobial and anti-inflammatory properties, offered significant protection from severe oxidative stress and inflammation and ameliorated the general well-being of mice against the toxic outcome of PQ.

Nanoporous ZnO/eosinY films prepared by electrochemical self-assembly have already shown promising characteristics for use in dye-sensitized solar cells, such as ease of preparation (no need for high-temperature sintering) and high dye loading. In this study, electron transport and back reaction in these films have been investigated by intensity modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). In contrast to sintered colloidal ZnO films, electrodeposited ZnO/eosinY films exhibit electron transit times (τD) that are much shorter than electron lifetimes (τn), leading to very efficient electron collection. The shorter transit times in the electrodeposited layers are due in part to the fact that the films are very thin, but in addition the electron diffusion coefficients are higher than in sintered colloidal ZnO films. Although the unusually high dye concentration in the electrochemically self-assembled film allows efficient light harvesting, it was found that not all dye molecules inject electrons. The low injection efficiency is probably due to the formation of dye aggregates.

A brief outline of certain features of the chemiosmotic hypothesis of the mechanism of free-energy transfer between the reactions of electron transport and adenosine triphosphate synthesis catalysed by biological membranes is given. Pulses of electron transport induced by the addition of small quantities of oxygen to suspensions of the bacterium Paracoccus denitrificans lead to vectorial H+ movements into the aqueous phase external to the organisms, where they may be detected with a glass pH electrode. The stoichiometry of the number of protons translocated into the bulk phase external to the organisms, per oxygen atom reduced, is essentially unchanged when the amount of oxygen reduced is varied, in a manner inconsistent with the predictions of the chemiosmotic-coupling hypothesis. These and other observations lead to the view that the energy-coupling proton-transfer processes utilised in reactions such as electron-transport phosphorylation are confined to the membrane phase. Mechanisms which most easily account for this are discussed.

Formation of ATP in photosynthesis takes place at the expense of free energy stored in the gradient of protons across the thylakoid membrane. Set up of the proton gradient is accomplished by the light‐driven electron transport reactions. The stoichiometry of H+ translocation across the thylakoid membrane is determined with respect to electron flow and ATP synthesis. Direct information is obtained on the basis of the H+ flux measurement. Depending on the experimental conditions two or three H+ are translocated from outside into the aqueous inner phase of the thylakoid vesicles for each electron which is transferred through the electron transport chain. Three H+ are translocated from inside to outside across the ATPase for each ATP molecule which is synthesized. Mechanistic and energetic consequences are discussed.