Photooxidation reactions of diphenylcarbazide and their DCMU-sensitivity in thylakoids of the blue-green alga Oscillatoria chalybea

Thylakoids of Oscillatoria chalybea are able to split water. The Hill reaction of these thylakoids is sensitive to DCMU. Diphenylcarbazide can substitute for water as the electron donor to photosystem II with these fully functioning thylakoids. However, the diphenylcarbazide photooxidation is completely insensitive to 3-(3,4-dichlorophenyl)-N-N-dimethyl urea (DCMU) at high diphenylcarbazide concentrations. In with Tris-treated Oscillatoria thylakoids the water splitting capacity is lost and diphenylcarbazide restores electron transport through photosystem II as occurs with higher plant chloroplasts. However, also these photoreactions are insensitive to DCMU. If diphenylcarbazide acts in Oscillatoria as an electron donor to photosystem II the result suggests that diphenylcarbazide feeds in its electrons behind the DCMU inhibition site. This in turn indicates that in Oscillatoria the site of inhibition of DCMU is on the donor side of photosystem II.Abbreviations Used DCMU 3-(3,4-dichlorophenyl)-N-N-dimethyl urea - DPC diphenylcarbazide - DCPiP 2,6-dichlorophenol indophenol - TMB tetramethyl benzidine - A-2-sulf anthraquinone-2-sulfonate     

Photosynthetic activities of a membrane preparation of the thermophilic cyanobacterium Mastigocladus laminosus

Photosynthetically active membranes have been prepared from the thermophilic cyanobacterium Mastigogladus laminosus by treatment with lysozyme. The membranes were active in electron transport through photosystem I and II as well as in photophosphorylation and proton uptake. Cells were grown at 40°, 45° and 55°C respectively. The temperature optimum of oxygen evolution of whole cells was about 10°C higher than the growth temperature. In isolated membranes the temperature optimum for cyclic photophosphorylation was identical to the growth temperature of the cells whereas the optimum for photosystem II electron transport never exceeded 40°C. Photophosphorylation was inhibited by N, N-dicyclohexyl carbodiimide (DCCD), carbonyl-cyanide-m-chlorophenylhydrazone and NH₄Cl, whereas proton uptake was enhanced by DCCD. Electron transport was slightly inhibited by these treatments. The membranes could be stored for several weeks at-20°C in 50% glycerol without any loss in the activities.Abbreviations DPIP 2,6-dichlorophenolindophenol - CCCP Carbonyl-cyanide-m-chlorophenylhydrazone - DCCD N,N-dicyclohexyl carbodiimide - PMS N-methylphenazonium methosulfate - DCMU 3-(3-4-dichlorophenyl)-1,1-dimethylurea - TMP 20 mM Tris-HCl buffer pH 7.8, 10 mM MgCl₂, 5 mM phosphate buffer pH 7.8     

Correction of the published sequence for the human proteolipid protein gene

Summary In the human proteolipid protein gene, the base sequence of the intronic region 5 to exon 6 was found to be 5-ctctttcattttcctgcag-3 and not 5-ctctttt-cattttcctgcag-3 as previously reported.     

Membrane proteins related to anion permeability of human red blood cells

Summary (³H)DIDS (4,4-diisothiocyano-2,2-ditritiostilbene-disulfonate) was used as a convalent label for membrane sites involved in anion permeability. The label binds to a small, superficially located population of sites, about 300,000 per cell, resulting in almost complete inhibition of anion exchange. The relationship of biding to inhibition is linear suggesting that binding renders each site nonfunctional. In the inhibitory range less than 1% of the label is associated with lipids but at higher concentrations of DIDS, the fraction may be as high as 4%. In ghosts, however, treatment with (³H)DIDS results in extensive labeling of lipids. In cells, a protein fraction that behavens on SDS acrylamide gels as thought its molecular weight is 95,000 daltons (95K) is predominatly labeled by (³H)DIDS. The only other labeled protein is the major sialoglycoprotein which contains less than, 5% of the total bound (³H)DIDS. Because of the linear relationship of binding to inhibition and the unique architecture of the site, it is suggested that the (³H)DIDS-binding site of the 95K protein is the substrate binding site of the anion transport system. The 95K protein is asymmetrically arranged in the membrane with the sites arranged on the outer face accessible to agent in the medium. In leaky ghost, only a few additional binding sites can be reached from the inside of the membrane in the 95K protein, in contrast to the extensive labeling of other membrane proteins in ghosts as compared to cells.Abbreviations DADS 4,4-Diamino-2,2-dihydrostilbene disulfonic acid - DIDS 4,4-Diisothiocyano-2,2-stilbene disulfonic acid - (³H)DADS 4,4-Diamino-2,2-ditritiostilbene disulfonic acid - (³H)DIDS 4,4-Diisothiocyano-2,2-ditritiostilbene disulfonic acid     

Selective photobleaching of PSI-related chlorophylls in heat-stressed pea chloroplasts

Measurements of electron transport activity point to the occurrence of major changes in the organisation of the photosynthetic apparatus of heat-stressed chloroplasts. One of the consequences of these changes is shown to be a greatly increased susceptibility of chlorophyll to photobleaching. Despite the fact that the threshold temperature for this photobleaching coincides closely with that for the inhibition of PSII activity, the bleached components were found to be specifically associated with PSI. This increased susceptibility of PSI pigments to photobleaching is shown to be a direct consequence of an interruption of the flow of reductants from PSII to PSI that would normally protect PSI from photooxidation.Abbreviations PSI photosystem I - PSII photosystem II - chl a chlorophyll a - chl b chlorophyll b - LHCP chlorophyll a/b light-harvesting protein - CP₁ P700-chlorophyll a protein - DCMU 3-(34 dichlorophenyl)-11-dimethylurea - DCPIP dichlorophenolindophenol - Fecy potassium ferricyanide - MV methyl viologen Biochemistry Department, King's College (KQC), University of London     

Freezing damage and frost tolerance of the photosynthetic apparatus studied with isolated mesophyll protoplasts of Valerianella locusta L.

Mesophyll protoplasts were isolated from unhardened and cold-acclimated leaves of Valerianella locusta L. and subjected to freeze-thaw treatment. To evaluate the extent and course of freezing injury, photosynthetic reactions of whole protoplasts and of free thylakoid membranes, liberated from protoplasts by osmotic lysis, were measured. In addition, the integrity of the protoplasts was determined by microscopy. The results reveal an increased frost tolerance of protoplasts isolated from acclimated leaves with respect to all parameters measured. CO₂-dependent O₂ evolution (representing net photosynthetic CO₂ fixation of protoplasts) was the most freezing-sensitive reaction; its inhibition due to freeze-thaw treatment of protoplasts was neither correlated with disintegration of the plasma membrane, nor was it initiated by inactivation of the thylakoid membranes. The frost-induced decline of protoplast integrity was not closely correlated to thylakoid damage either. Freezing injury of the thylakoid membranes was manifested by inhibition of photosynthetic electron transport and photophosphorylation. Both photosystems were affected by freezing and thawing with strongest inhibition occurring in the water-oxidation system or at the oxidizing site of photosystem II. Photophosphorylation responded more sensitively to freezing stress than electron transport, although uncoupling (increased permeability of the thylakoid membranes to protons) was not a conspicuous effect. The data are discussed in relation to freezing injury in leaves and seem to indicate that frost damage in vivo is initiated at multiple sites.Abbreviations Chl chlorphyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCIP 2,6-dichlorophenolindophenol - DPC 1,5-diphenylcarbazide - Hepes 2-[4-(2-hydroxyethyl)-1-piperazinyl]-ethanesulfonic acid - MES 2-(N-morpholino)-ethanesulfonic acid - PS I photosystem I - PS II photosystem II     

Photosynthesis and plasmamembrane permeability properties of Prochloron

Photosynthetic carbon fixation of freshly isolated cells of Prochloron, the symbiont of Lissoclinum patella, proceeded at high rates (80–180 mol O₂·mgChl^-1·h^-1) in buffered seawater and showed a typical light response, saturating at about 300 E·m^-2·s^-1. However, in NaCl solutions osmotically equivalent to seawater CO₂-dependent O₂ evolution ceased or was severely inhibited. Hypotonic or hypertonic conditions induce degrees of swelling or shrinkage, respectively, apparently causing similar increases in the plasmamembrane's permeability to ferricyanide. Initially high, but rapidly declining, rates of electron transport were observed when the cells were suspended in distilled water. This inhibition was not caused by rupture of the cells, indicating instead diffusive loss of some essential factor(s) which normally exchange easily and rapidly between the cells and/or the host environment. Such rapid exchange may be part of the mechanism of this symbiosis and, if not adequately understood, may frustrate attempts to culture Prochloron away from its host.Abbreviations HEPES N-2-hydroxyethyl piperazine-N-2 ethane sulphonic acid - EPPS N-2-hydroxyethyl propane sulphonic acid - FeCN potassium ferricyanide - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - TMPD N,N,N,N,-tetramethyl-p-phenylenediamine - DCIP 2,6-dichlorophenol-indophenol - MV methylviologen - PS photosystem - Chl chlorophyll Publication No. 219 of the Australian Institute of Marine Science     

Studies on the molecular basis of H+ translocation by cytochromec oxidase

We report here studies which characterize further the interaction ofN,N-dicyclohexylcarbodiimide with cytochromec oxidase leading to inhibition of H⁺ translocation by the enzyme. Further evidence is presented to show that the inhibition results from a real interaction of DCCD with the enzyme and cannot be accounted for by uncoupling and, contrary to recent criticisms, this interaction occurs specifically with subunit III of the enzyme even at relatively high inhibitor-to-enzyme stoichiometries. Use of a spin-label analogue of DCCD has enabled us to demonstrate that the carbodiimide-binding site is highly apolar and may not lie on the pathway of electron transfer.Abbreviations DCCD N,N-dicyclohexylcarbodiimide - NCCD N-(2, 2, 6, 6-tetramethylpiperidyl-1-oxyl)-N-(cyclohexyl)carbodiimide - Hepes 2-(N-2-hydroxyethylpiperazin-N-yl) ethane sulfonate - TMPD N,N,N,N-tetramethylphenylenediamine     

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     

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     

Multiple anion effects on photosystem II in chloroplast membranes

We investigated the activity of several anions at various sites on photosystem II, in particular those associated with the Cl^- effect (anion binding-site I) and the HCO₃ ^- effect (anion binding-site II). Chlorophyll a fluorescence changes were used to monitor partial photosystem II reactions either in the oxygen-evolving mechanism or involving endogenous quinone electron acceptors. We find that anions such as NO₃ ^-, HCO₃ ^-, HCO₂ ^-, F^-, NO₂ ^-, and acetate can, depending on conditions, bind to either anion binding-site I, anion binding-site II, or both sites simultaneously. The anions N₃ ^- and Au(CN)₂ ^- are exceptions. In their presence, oxygen-consumption reactions are enhanced. The results demonstrate that an exclusive site or mode of action of an anion on photosystem II cannot be determined by measuring the Hill reaction alone. Anion interactions with photosystem II are shown to be very complex and, therefore, caution is advisable in interpreting related experiments. Carbonic anhydrase associated with photosystem II was also investigated as a possible target for some anion effects. In Cl^--depleted thylakoids, NO₃ ^-, stimulated both electron transport and carbonic anhydrase activity at low concentrations, while higher concentrations inhibited both. However, carbonic anhydrase was more sensitive to inhibition by NO₃ ^- than was electron flow. Possible interpretations are discussed; the electron transport and carbonic anhydrase activity appear not to be functionally linked.Abbreviations ABSI Anion binding-site(s) I associated with the oxygen-evolving mechanism - ABSII Anion binding-site(s) II, which controls quinone-related reactions on the electron-acceptor side of photosystem II - OAc^- Acetate - Chl Chlorophyll - DCMU 3—(3,4-dichlorophenyl)-1,1-dimethyl urea - DCBQ 2,6-dichloro-p-benzoquinone - DMBQ 2,5-dimethyl-p-benzoquinone - Mes 2-[N-morpholino]ethanesulphonic acid - Mops 3-[N-morpholino]propanesulphonic acid - Tes N-Tris[hydroxymethyl]methyl-2-aminoethanesulphonic acid - Tricine N-Tris[hydroxymethyl]methylglycine     

Observations on the reduction of non-activated carboxylates by Clostridium formicoaceticum with carbon monoxide or formate and the influence of various viologens

Crude extracts or supernatants of broken cells of Clostridium formicoaceticum reduce unbranched, branched, saturated and unsaturated carboxylates at the expense of carbon monoxide to the corresponding alcohols. The presence of viologens with redox potentials varying from E ₀=-295 to-650 mV decreased the rate of propionate reduction. The more the propionate reduction was diminished the more formate was formed from carbon monoxide. The lowest propionate reduction and highest formate formation was observed with methylviologen. The carbon-carbon double bond of E-2-methyl-butenoate was only hydrogenated when a viologen was present. Formate as electron donor led only in the presence of viologens to the formation of propanol from propionate. The reduction of propionate at the expense of a reduced viologen can be followed in cuvettes. With respect to propionate Michaelis Menten behavior was observed. Experiments are described which lead to the assumption that the carboxylates are reduced in a non-activated form. That would be new type of biological reduction.Non-standard abbreviations glc Gas liquid chromatography - HPLC high performance liquid chromatography - RP reverse phase; Mediators (the figures in parenthesis of the mediators are redox potentials E ₀ in mV) - CAV²⁺ carbamoylmethylviologen, 1,1-carbamoyl-4,4-dipyridinium dication (E ₀=-296 mV) - BV²⁺ benzylviologen, 1,1-dibenzyl-4,4-dipyridinium dication (E ₀=-360 mV) - MV methylviologen, 1,1-dimethyl-4,4-dipyridinium-dication (E ₀=-444 mV) - DMDQ²⁺ dimethyldiquat, 4,4-dimethyl-2,2-dipyridino-1,1-ethylendication (E ₀=-514 mV) - TMV²⁺ tetramethylviologen, 1,1,4,4-tetramethyl-4,4-dipyridinium dication (E ₀=-550 mV) - PDQ²⁺ propyldiquat, 2,2-dipyridino-1,1-propenyl dication (E ₀=-550 mV) - DMPDQ²⁺ dimethylpropyldiquat, 4,4-dimethyl-2,2-dipyridino-1,1-propenyl dication (E ₀=-656 mV) - PN productivity number=mmol product (obtained by the uptake of one pair of electrons) x (biocatalyst (dry weight) kg)^-1×h^-1     

Photosynthetic electron transport and carbon-reduction-cycle enzyme activities under long-term drought stress in Casuarina equisetifolia Forst. & Forst.

The inhibition of photosynthetic electron transport and the activity of photosynthetic carbon reduction cycle (PCR) enzymes under long-term water stress after slow dehydration was studied in non-nodulated Casuarina equisetifolia Forst. & Forst. plants. Initially, drought increased the fraction of closed Photosystem II (PS II) reaction centres (lowered qP) and decreased the quantum yield of PS II electron transport (_PSII) with no enhancement of non-radiative dissipation of light energy (qN) because it increased the efficiency of electron capture by open PS II centres (F_v/F_m). As drought progressed, F_v/F_m fell and the decrease in _PSII was associated with an increased qN. The kinetics of dark relaxation of fluorescence quenching pointed to an increase in a slowly-relaxing component under drought, in association with increased contents of zeaxanthin and antheraxanthin. Total NADP-dependent malate dehydrogenase activity increased and total stromal fructose-1,6-bisphosphatase activity decreased under drought, while the activation state of these enzymes remained unchanged. Water stress did not alter the activity and the activation state of ribulose bisphosphate carboxylase oxygenase.     

A high-affinity iron transport system of Rhizobium meliloti may be required for efficient nitrogen fixation in planta

We have analyzed the ability of single site insertion mutants of Rhizobium meliloti 1021 defective in various components of a high-affinity iron transport system to produce nodules, fix nitogen and promote plant growth. Our results indicate that a high-affinity iron transport system may significantly increase the ability of the differentiated form of the bacterium to fix nitrogen and induce an increase in plant growth.Abbreviations EDDA ethylenediamine-N,N-bis(2-hydroxyphenylacetic acid) - CAS chrome azurol S     

Evidence for chloride dependent potassium and water transport induced by hyposmotic stress in erythrocytes of the marine teleost,Opsanus tau

Summary Red blood cells of the marine teleost,Opsanus tau (oyster toadfish), were characterized as to their normal hemoglobin, ion and water contents. Cells were exposed to ouabain containing, hyposmotic salt solutions (osmolarity reduced to 2/3 of normal) in which the cation or anion composition was varied. It was found that the initial cell volume expansion due to water influx was independent of the anion present. However, a secondary volume reduction was dependent on the presence of chloride or bromide anions. During volume reduction, cellular potassium and chloride ion contents fell by about equal amounts. Potassium loss was commensurate to the total amount of potassium ions detected extracellularly about 1.5h after the initial osmotic shock. No major changes were seen in the cellular sodium ion contents. When chloride ions within the cells and in the suspending medium were replaced by nitrate, iodide or thiocyanate, the cells failed to return to volumes close to those of isosmotically suspended controls, and the cellular potassium content also remained constant. In hypotonic potassium chloride the cells failed to extrude potassium chloride and water, and hence retained their expanded volume. Neither potassium loss nor volume decrease occurred in cells swollen in hypotonic sodium chloride media containing furosemide or 4,4 diisothiocyano-2,2-stilbene-disulfonic acid (DIDS). These two compounds are known inhibitors of monovalent cation cotransport and anion self exchange, respectively, in mammalian red cells. Hence toadfish red cells respond to osmotic swelling primarily by activation of an ouabain-insensitive, chloride dependent potassium transport system which is sensitive to inhibition by furosemide and DIDS.     

Comparison of Photosystem-I and Photosystem-II activities of spheroplasts from normal and photobleached Anabaena cylindrica

The analysis of photochemical activities of Photosystem I and Photosystem II in spheroplasts from normal and photobleached Anabaena cylindrica showed an increase in Photosystem II activity relative to Photosystem I in photobleached cells. We suggest that the reasons for this modification in photochemical activity are, (i) a rearrangement of pigments between the two photosystems, and (ii) improved functional condition of the photosynthetic units in Photosystem II.Abbreviations PSI Photosystem I - PSII Photosystem II - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea - MV methylviologen - DCPIP 1,6-dichlorphenol indophenol - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - FeCN Ferricyanide - APC anophycocyanin - PC phycocyanin     

Photosynthetischer Elektronentransport der Alge Bumilleriopsis während der Zellentwicklung

Summary The alga Bumilleriopsis filiformis Vischer (Xanthophyceae) was synchronized by light intensity combined with temperature changes. During the 48-h cell cycle there is a stage of low cellular photosynthetic activity in the 34th hour after start of the cycle and one of high activity between the 39th and 41th hour. These activities were compared with the p-benzoquinone mediated Hill reaction of non-homogenized cells and electron transport rates measured with carefully isolated chloroplast material. Ferricyanide and methylviologen reduction was tested with water as donor and photosystem I reactions with reduced dichloro-phenolindophenol and diaminodurene. The influence of superoxide dismutase and ascorbate was examined. The data show parallel changes in the activities of electron transport and cellular photosynthesis during cell development and indicate corresponding alteration not only in the activity of photosystem II but also in that of system I.

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Abkürzungen pBQ p-Benzochinon - Chl Chlorophyll - DAD 2,3,5,6-Tetramethyl-p-phenylendiamin (Diaminodurol) - DCMU 3-(3,4-Dichlorphenyl)-1,1-dimethylharnstoff - DCIP 2,6-Dichlorphenolindophenol - FCCP Carbonylcyanid-p-trifluormethoxyphenyl-hydrazon - FeCy Kaliumhexacyano-(III)-ferrat - LST (Stark)-Licht-Schwachlicht-Temperaturwechsel (zur Synchronisierung) - MV Methylviologen (1,1-Dimethyl-4,4-dipyridylium-dichlorid) - PS-I, PS-II Photosystem I bzw, II - SOD Superoxid-Dismutase - TRICIN N-Tris-(hydroxymethyl)-methylglycin (Puffer)     

The effects of chilling in the dark and in the light on photosynthesis of tomato: electron transfer reactions

Exposure of tomato plants (Lycopersicon esculentum Mill. cv. Floramerica) to chilling temperatures in the dark for as little as 12 h resulted in a sizable inhibition in the rate of light- and CO₂-saturated photosynthesis. However, when photosynthesis was measured at low light intensity, the inhibition disappeared and the quantum yield of CO₂ reduction was diminished only slightly. Chilling the tomato plants under strong illumination caused an even more rapid and severe decline in the rate of light- and CO₂-saturated photosynthesis, accompanied by a large decline in the quantum efficiency. Sizeable inhibition of photosystem II activity was observed only after dark exposures to low temperature of grater than 16 h. No inhibition of photosystem I electron transfer capacity was observed even after 40 h of dark chilling. Chilling under high light resulted in a rapid decline in both photosystem I and photosystem II electron transfer capacity as well as in significant reaction center inactivation.Regardless of whether the chilling exposure was in the presence or absence of illumination and regardless of its duration, the electron transfer capacity of thylakoid membranes isolated from the treated plants was always in excess of that necessary to support light- and CO₂-saturated photosynthesis. Thus, in neither case of chilling inhibition of photosynthesis does it appear that impaired electron transfer capacity represents a significant rate limitation to whole plant photosynthesis.Abbreviations BSA bovine serum albumin - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCMU 3-(3,4-Dichlorophenyl)-1,1-dimethylurea - DHQ duroquinol - EDTA ethylene-diamine-tetraacetic acid - HEPES N-2-hydroxylpiperazine-N-2-ethanesulfonic acid - MES 2-(N-Morpholino)ethanesulfonic acid - MV methylviologen - PS I & II photosystems I and II - PD_OX p-phenylenediimine (oxidized) - TMPD N,N,N,N-tetramethyl-p-phenylenediamine     

Inhibition of photosynthetic reactions by light

Illumination of isolated intact chloroplasts of Spinacia oleracea L. for 10 min with 850 W m^-2 red light in the absence of substrate levels of bicarbonate caused severe inhibition of subsequently measured photosynthetic activities. The capacity of CO₂-dependent O₂ evolution and of non-cyclic electron transport were impaired to similar degrees. This photoinactivation was prevented by addition of bicarbonate which allowed normal carbon metabolism to proceed during preillumination. Photoinhibition of electron transport was observed likewise upon illumination of intact or broken chloroplasts when efficient electron acceptors were absent. Addition of uncouplers did not influence the extent of inhibition. Studies of partial electron-transport reactions indicated that the activity of both photosystems was affected by light. In addition, the water-oxidation system or its connection to photosystem II seemed to be impaired. Preillumination did not cause uncoupling of photophosphorylation. Chlorophyll-fluorescence data obtained at room temperature and at 77 K are consistent with the view that photosystem-II reaction centers were altered. Addition of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6) or 1,4-diazabicyclo(2,2,2)octane to isolated thylakoids prior to preillumination substantially diminished photoinhibition. This result shows that reactive oxygen species were involved in the damage. It is concluded that bright light, which normally does not damage the photosynthetic apparatus, may exert the described destructive effects under conditions that restrict metabolic turnover of photosynthetic energy.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PSI photosystem I - PSII photosystem II     

Polymerization of amino acids containing nucleotide bases

Summary We have prepared the nucleoamino acids 1-(3-amino, 3-carboxypropyl)uracil (3) and 9-(3-amino, 3-carboxypropyl)adenine (4) as (l)-enantiomers and as racemic mixtures. When3 or4 is suspended in water and treated with N,N-carbonyldiimidazole, peptides are formed in good yield. The products formed from the (l)-enantiomers are hydrolyzed to the monomeric amino acids by pronase.Attempts to improve the efficiency of these oligomerizations by including a polyuridylate template in the reaction mixture were not successful. Similarly, oligomers derived from the (l)-enantiomer of3 did not act as templates to facilitate the oligomerization of4.