The effects of copper ions on the synthesis of periplasmic and membrane proteins in Acidithiobaeillus ferrooxidans as analyzed by SDS-PAGE and 2D-PAGE

The effects of 200 mM copper ions on the synthesis of membrane and periplasmic proteins were investigated in iron-grown cells of Acidithiobacillus ferrooxidans (At. ferrooxidans). Total membrane protein profiles of cells grown in the absence of copper ions (unadapted cells) and in the presence of copper ions (copper-adapted cells) were compared by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Crude preparations of outer membrane and periplasmic proteins were analyzed by SDS-PAGE. The synthesis of proteins was diminished or increased in the presence of copper ions. Low molecular weight proteins (< 14 kDa) were significantly repressed by copper. These proteins are probably acidic proteins located in the outer membrane. An over-expression of a periplasmic protein of about 17 kDa was detected in the copper-adapted cells and was assumed to be rusticyanin, a 16.5-kDa periplasmic copper protein present in At. ferrooxidans cells and involved in the electron-transport chain of the iron oxidation pathway. To our knowledge, this is the first report of a possible involvement of the rusticyanin and outer membrane proteins in the mechanism of copper resistance in At. ferrooxidans. (C) 2003 Elsevier B.V. All rights reserved.

Amicarbazone, a New Photosystem II Inhibitor

Amicarbazone is a new triazolinone herbicide with a broad spectrum of weed control. The phenotypic responses of sensitive plants exposed to amicarbazone include chlorosis, Stunted growth, tissue necrosis, and death. Its efficacy as both a foliar- and root-applied herbicide suggests that absorption and translocation of this compound is very rapid. This new herbicide is a potent inhibitor of photosynthetic electron transport, inducing chlorophyll fluorescence and interrupting oxygen evolution ostensibly via binding to the Q(B) domain of photosystem II (PSII) in a manner similar to the triazines and the triazinones classes of herbicides. As a result, its efficacy is susceptible to the most common form of resistance to PSII inhibitors. Nonetheless, amicarbazone has a good selectivity profile and is a more potent herbicide than atrazine, which enables its use at lower rates than those of traditional photosynthetic inhibitors.

Abamectin affects the bioenergetics of liver mitochondria: A potential mechanism of hepatotoxicity

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Improved Conductivity Induced by Photodesorption in SnO2 Thin Films Grown by a Sol-Gel Dip Coating Technique

Thin films of undoped and Sb-doped SnO2 have been prepared by a sol-gel dip-coating technique. For the high doping level (2-3 mol% Sb) n-type degenerate conduction is expected, however, measurements of resistance as a function of temperature show that doped samples exhibit strong electron trapping, with capture levels at 39 and 81 meV. Heating in a vacuum and irradiation with UV monochromatic light (305 nm) improve the electrical characteristics, decreasing the carrier capture at low temperature. This suggests an oxygen related level, which can be eliminated by a photodesorption process. Absorption spectral dependence indicates an indirect bandgap transition with Eg ≅ 3.5 eV. Current-voltage characteristics indicate a thermionic emission mechanism through interfacial states.

Numerical study of the spherically symmetric Gross-Pitaevskii equation in two space dimensions

The Gross-Pitaevskii equation for Bose-Einstein condensation (BEC) in two space dimensions under the action of a harmonic oscillator trap potential for bosonic atoms with attractive and repulsive interparticle interactions was numerically studied by using time-dependent and time-independent approaches. In both cases, numerical difficulty appeared for large nonlinearity. Nonetheless, the solution of the time-dependent approach exhibited intrinsic oscillation with time iteration which is independent of space and time steps used in discretization.

Photosynthetic responses to temperature in tropical lotic macroalgae

A comparative analysis of the photosynthetic responses to temperature (10-30°C) was carried out under short-term laboratory conditions by chlorophyll fluorescence and oxygen (O2) evolution. Ten lotic macroalgal species from southeastern Brazil (20°11-20°48′S, 49°18-49°41′W) were tested, including Bacillariophyta, Chlorophyta, Cyanophyta, Rhodophyta and Xanthophyta. Temperature had significant effects on electron transport rate (ETR) only for three species (Terpsinoe musica, Bacillariophyta; Cladophora glomerata, Chlorophyta; and C. coeruleus, Rhodophyta), with highest values at 25-30°C, whereas the remaining species had no significant responses. It also had similar effects on non-photochemical quenching and ETR. Differences in net photosynthesis/dark respiration ratios at distinct temperatures were found, with an increasing trend of respiration with higher temperatures. This implies in a decreasing balance between net primary production and temperature, representing more critical conditions toward higher temperatures for most species. In contrast, high net photosynthesis and photosynthesis/dark respiration ratios at high and wide ranges of temperature were found in three species of green algae, suggesting that these algae can be important primary producers in lotic ecosystems, particularly in tropical regions. Optimal photosynthetic rates were observed under similar environmental temperatures for five species (two rhodophytes, two chlorophytes and one diatom) considering both techniques, suggesting acclimation to their respective ambient temperatures. C. coeruleus was the only species with peaks of ETR and O 2 evolution under similar field-measured temperatures. All species kept values of ETR and net photosynthesis close to the optimum under a broad range of temperatures. Increased non-photochemical quenching, as a measure of thermal dissipation of excess energy, toward higher temperatures was observed in some species, as well as positive correlation of non-photochemical quenching with ETR, and were interpreted as two mechanisms of adaptation of the photosynthetic apparatus to temperature changes. Different optimal temperatures were found for individual species by each technique, generally under lower temperatures by O2 evolution, indicating dependence on distinct factors: increases in temperature generally induced higher ETR due to increased enzymatic activity, whereas increments of enzymatic activity were compensated by increased respiration and photorespiration leading to decreases in net photosynthesis.

Horseradish peroxidase-catalyzed oxidation of rifampicin: Reaction rate enhancement by co-oxidation with anti-inflammatory drugs

The tuberculostatic drug rifampicin has been described as a scavenger of reactive species. Additionally, the recent demonstration that oral therapy with a complex of rifampicin and horseradish peroxidase (HRP) was more effective than rifampicin alone, in an animal model of experimental leprosy, suggested the importance of redox reactions involving rifampicin and their relevance to the mechanism of action. Hence, we studied the oxidation of rifampicin catalyzed by HRP, since this enzyme may represent the prototype of peroxidation-mediated reactions. We found that the antibiotic is efficiently oxidized and that rifampicin-quinone is the product, in a reaction dependent on both HRP and hydrogen peroxide. The steady-state kinetic constants Km app (101±23 mmol/l), Vmax app (0.78±0.09 μmol/l·s-1) and kcat (5.1±0.6 s-1) were measured (n=4). The reaction rate was increased by the addition of co-substrates such as tetramethylbenzidine, salicylic acid, 5-aminosalicylic acid and paracetamol. This effect was explained by invoking an electron-transfer mechanism by which these drugs acted as mediators of rifampicin oxidation. We suggested that this drug interaction might be important at the inflammatory site. © 2005 Pharmaceutical Society of Japan.

Eucalyptus ESTs corresponding to the enzyme glutamine synthetase and the protein D1, sites of action of herbicides that cause oxidative stress

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

COX24 codes for a mitochondrial protein required for processing of the COX1 transcript

In most strains of Saccharomyces cerevisiae the mitochondrial gene COX1, for subunit 1 of cytochrome oxidase, contains multiple exons and introns. Processing of COX1 primary transcript requires accessory proteins factors, some of which are encoded by nuclear genes and others by reading frames residing in some of the introns of the COX1 and COB genes. Here we show that the low molecular weight protein product of open reading frame YLR204W, for which we propose the name COX24, is also involved in processing of COX1 RNA intermediates. The growth defect of cox24 mutants is partially rescued in strains harboring mitochondrial DNA lacking introns. Northern blot analyses of mitochondrial transcripts indicate cox24 null mutants to be blocked in processing of introns aI2 and aI3. The dependence of intron aI3 excision on Cox24p is also supported by the growth properties of the cox24 mutant harboring mitochondrial DNA with different intron compositions. The intermediate phenotype of the cox24 mutant in the background of intronless mitochondrial DNA, however, suggests that in addition to its role in splicing of the COX1 pre-mRNA, Cox24p still has another function. Based on the analysis of a cox14-cox24 double mutant, we propose that the other function of Cox24p is related to translation of the COX1 mRNA. © 2006 by The American Society for Biochemistry and Molecular Biology, Inc.

Kinetic study of the plastoquinone pool availability correlated with H2O2 release in seawater and antioxidant responses in the red alga Kappaphycus alvarezii exposed to single or combined high light, chilling and chemical stresses

Under biotic/abiotic stresses, the red alga Kappaphycus alvarezii reportedly releases massive amounts of H2O2 into the surrounding seawater. As an essential redox signal, the role of chloroplast-originated H2O2 in the orchestration of overall antioxidant responses in algal species has thus been questioned. This work purported to study the kinetic decay profiles of the redox-sensitive plastoquinone pool correlated to H2O2 release in seawater, parameters of oxidative lesions and antioxidant enzyme activities in the red alga Kappaphycus alvarezii under the single or combined effects of high light, low temperature, and sub-lethal doses of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), which are inhibitors of the thylakoid electron transport system. Within 24 h, high light and chilling stresses distinctly affected the availability of the PQ pool for photosynthesis, following Gaussian and exponential kinetic profiles, respectively, whereas combined stimuli were mostly reflected in exponential decays. No significant correlation was found in a comparison of the PQ pool levels after 24 h with either catalase (CAT) or ascorbate peroxidase (APX) activities, although the H2O2 concentration in seawater (R = 0.673), total superoxide dismutase activity (R = 0.689), and particularly indexes of protein (R = 0.869) and lipid oxidation (R = 0.864), were moderately correlated. These data suggest that the release of H2O2 from plastids into seawater possibly impaired efficient and immediate responses of pivotal H2O2-scavenging activities of CAT and APX in the red alga K. alvarezii, culminating in short-term exacerbated levels of protein and lipid oxidation. These facts provided a molecular basis for the recognized limited resistance of the red alga K. alvarezii under unfavorable conditions, especially under chilling stress. © 2006 Elsevier B.V. All rights reserved.

Photoacclimation in three species of freshwater red algae

Three freshwater Rhodophyta species (Audouinella eugenea, A. hermannii and Compsopogon coeruleus) were tested as to their responses (photosynthesis, growth and pigment concentration) to two irradiances (low light, LL, 65 μmol m -2 s-1 and high light, HL, 300 μmol m-2 s-1) and two periods (short time, ST, 4 d, and long time, LT, 28 d). Higher growth rates were consistently observed at LL but significant differences were observed only for A. hermannii. Higher values of photoinhibition at LL were found for the three species, which is consistent with the dynamic photoinhibition as a reversible photoprotective mechanism against high irradiance. Light-induced decreases of effective quantum yield (EQY) were observed in the three species consisting of pronounced decreases from LL to HL. Rapid increases of non-photochemical quenching (NPQ) were observed mainly at LL, indicating energy dissipation by reaction centers. Results revealed distinct photoacclimation strategies to deal with high irradiances: the two Audouinella species had only characteristics of shade-adapted algae: acclimation by changes of size of photosy stem units (PSU) under LT and by PSU number under ST; higher values of the photoinhibition parameter (β) and NPQ, and lower values of EQY at LL; higher recovery capacity of potential quantum yield (PQY) at LL and under ST; highly significant positive correlation of electron transport rate (ETR) with NPQ. In addition, C. coeruleus mixed some characteristics of sun-adapted algae: acclimation by changes of PSU number under LT and by PSU size under ST; higher recovery capacity of EQY than the other two species; weak or no correlation of ETR with NPQ. Thus, these characteristics indicate that C. coeruleus cope with high irradiances more efficiently than the Audouinella species.

Structural control of photoluminescence of four poly(urethane-urea-co-1,3,5-triazine)s: Synthesis and characterization

A series of segmented poly(urethane-urea)s containing 1,3,5 triazine in the hard block and hexamethylene spacers in the soft block was prepared. The hard to soft segment ratio was varied systematically, to afford a series of polymers in which the chromophore concentration varied from 4.2% to 18.1%. Although triazine emission is located in the UV region, the films with higher content of the chromophore emitted a visible blue light (425 nm) when excited at the very red-edge of the absorption band. The photophysical properties of the materials were strongly dependent on the relative amount of triazine moieties along the main chain. Isolated moieties emit in copolymers with small amount of triazine groups, indicating that even though in solid state, these moieties tend to be apart. Two photophysical consequences were observed when the amount of triazine increases: there is some energy transfer process involving isolated moieties with consequent decrease of the lifetime and an additional red-edge emission attributed to aggregated lumophores. The mono-exponential decay observed for the isolated form is substituted by a bi-exponential decay of the aggregated species. The materials were not strong emitters, but since the N-containing triazine moieties are good electron transport groups, the polymers have potential application as electron transport enhancers in various applications. © 2006 Elsevier B.V. All rights reserved.

Nuclear mitochondrial-like sequences in ants: Evidence from Atta cephalotes (Formicidae: Attini)

Nuclear mitochondrial-like sequences (numts) are copies of mitochondrial DNA that have migrated to the genomic DNA. We present the first characterization of numts in ants, these numts being homologues to a mitochondrial DNA fragment containing loci the 3′ portion of the cytochrome oxidase I gene, an intergenic spacer, the tRNA leucine gene and the 5′ portion of the cytochrome oxidase II gene. All 67 specimens of Atta cephalotes (Hymenoptera: Formicidae: Attini) investigated had these homologues, which are within two monophyletic groups that we called numt1 and numt2. Numt1 and numt2 sequences are less variable than mitochondrial sequences and released from the severe purifying selection constraining the evolution of mitochondrial genes. Their formation probably involved bottlenecks related to two distinct transfer events of ancient and fast evolving mitochondrial DNA fragments to comparative slowly evolving nuclear DNA regions. © 2007 The Authors.

The electrochemical reduction of the purines guanine and adenine at platinum electrodes in several room temperature ionic liquids

The reduction of guanine was studied by microelectrode voltammetry in the room temperature ionic liquids (RTILs) N-hexyltriethylammonium bis (trifluoromethanesulfonyl) imide [N6,2,2,2][N(Tf)2], 1-butyl-3-methylimidazolium hexafluorosphosphate [C4mim][PF6], N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide [C4mpyrr][N(Tf)2], 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4mim][N(Tf)2], N-butyl-N-methyl-pyrrolidinium dicyanamide [C4mpyrr][N(NC)2] and tris(P-hexyl)-tetradecylphosphonium trifluorotris(pentafluoroethyl)phosphate [P14,6,6,6][FAP] on a platinum microelectrode. In [N6,2,2,2][NTf2] and [P14,6,6,6][FAP], but not in the other ionic liquids studied, guanine reduction involves a one-electron, diffusion-controlled process at very negative potential to produce an unstable radical anion, which is thought to undergo a dimerization reaction, probably after proton abstraction from the cation of the ionic liquid. The rate of this subsequent reaction depends on the nature of the ionic liquid, and it is faster in the ionic liquid [P14,6,6,6][FAP], in which the formation of the resulting dimer can be voltammetrically monitored at less negative potentials than required for the reduction of the parent molecule. Adenine showed similar behaviour to guanine but the pyrimidines thymine and cytosine did not; thymine was not reduced at potentials less negative than required for solvent (RTIL) decomposition while only a poorly defined wave was seen for cytosine. The possibility for proton abstraction from the cation in [N6,2,2,2][NTf2] and [P14,6,6,6][FAP] is noted and this is thought to aid the electrochemical dimerization process. The resulting rapid reaction is thought to shift the reduction potentials for guanine and adenine to lower values than observed in RTILs where the scope for proton abstraction is not present. Such shifts are characteristic of so-called EC processes where reversible electron transfer is followed by a chemical reaction. © 2009 Elsevier B.V.

Avaliação da absorção do amicarbazone e intoxicação em cana-de-açúcar e plantas daninhas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)