3,647 research outputs found
Proton and Iron Binding by the Cyanobacterial Toxin Microcystin-LR
No full textMDFRC item.Microcystins (MCs) are a group of hepatotoxins produced by cyanobacteria that have not had their functional role or the environmental factors that trigger production clearly determined. One suggestion is that microcystins are siderophores (i.e., ligands with an extremely high affinity with iron, typically with stability constants substantially greater than 10²⁵). In this work, we explore proton and iron binding with microcystin-LR (MC-LR). Using UV−visible spectroscopy and a HPLC peak retention time-based method, the two acid dissociation constants associated with the carboxylic groups of MC-LR were determined to be: pKa1 = 2.17 and pKa2 = 3.96. Cyclic voltammetry provides evidence for the formation of at least two FeIII-MC-LR complexes, with the FeIII reduction peak significantly shifted to more reducing potentials in the presence of MC-LR. These complexes have been interpreted as a rapidly formed initial complex (Complex 1) and a more stable, and slower forming, Complex 2. The stability constant for FeIII-MC-LR (Complex 2) was estimated to be approximately 10¹³ in 60% v/v MeOH/water at 0.1 M ionic strength. The electrochemical experiments provide no evidence for the formation of a complex between Fe2+ and MC-LR. Given that most MC-LR is released only upon cell lysis, and coupled with the moderate strength of the stability constant with FeIII determined in this study, it appears unlikely that that MC-LR is an extracellular siderophore. If MC-LR is involved in iron regulation in cyanobacteria, it is more likely as a shuttle for iron across the cell membrane or in intracellular processes
Proton and Iron Binding by the Cyanobacterial Toxin Microcystin-LR
No full textMDFRC item.Microcystins (MCs) are a group of hepatotoxins produced by cyanobacteria that have not had their functional role or the environmental factors that trigger production clearly determined. One suggestion is that microcystins are siderophores (i.e., ligands with an extremely high affinity with iron, typically with stability constants substantially greater than 10²⁵). In this work, we explore proton and iron binding with microcystin-LR (MC-LR). Using UV−visible spectroscopy and a HPLC peak retention time-based method, the two acid dissociation constants associated with the carboxylic groups of MC-LR were determined to be: pKa1 = 2.17 and pKa2 = 3.96. Cyclic voltammetry provides evidence for the formation of at least two FeIII-MC-LR complexes, with the FeIII reduction peak significantly shifted to more reducing potentials in the presence of MC-LR. These complexes have been interpreted as a rapidly formed initial complex (Complex 1) and a more stable, and slower forming, Complex 2. The stability constant for FeIII-MC-LR (Complex 2) was estimated to be approximately 10¹³ in 60% v/v MeOH/water at 0.1 M ionic strength. The electrochemical experiments provide no evidence for the formation of a complex between Fe2+ and MC-LR. Given that most MC-LR is released only upon cell lysis, and coupled with the moderate strength of the stability constant with FeIII determined in this study, it appears unlikely that that MC-LR is an extracellular siderophore. If MC-LR is involved in iron regulation in cyanobacteria, it is more likely as a shuttle for iron across the cell membrane or in intracellular processes
The role of Ruditapes philippinarum glutathione transferases in the metabolism of microcystin-LR
No full textNo abstracts are to be cited without prior reference to the author. Glutathione transferases (GSTs) are phase II enzymes involved in the microcystin (MC) induced detoxication processes. In this study we analyze and compare the metabolism of MC-LR by the cytosolic GSTs from gills and hepatopancreas of Ruditapes philippinarum. Cytosolic GSTs were purified by glutathione (GSH)–agarose affinity chromatography from exposed and non-exposed bivalves to MC-LR (100 µg/L) representing the inducible and constitutive (Basal) GST fractions, respectively. For each mixture, we examined the in vitro cytosolic GST inhibition efficiency of the conjugation of CDNB to GSH by MC-LR and characterize the inhibition mechanism. Results support the important role of GST enzymes in detoxification of MCs in bivalve mollusk
LR-drawings of ordered rooted binary trees and near-linear area drawings of outerplanar graph
No full textWe study a family of algorithms, introduced by Chan [SODA 1999], for drawing ordered rooted binary trees. Any algorithm in this family (which we name an LR-algorithm) takes in input an ordered rooted binary tree T with a root rT ,and recursively constructs drawings T L of the left subtree L of rT and TR of the right subtree R of rT ; then either it applies the left rule, i.e., it places L one unit below and to the left of rT , and R one unit below L with the root of R vertically aligned with rT , or it applies the right rule, it places R one unit below and to the right of rT , and L one unit below R with the root of L vertically aligned with rT . In both cases, the edges between rT and its children are represented by straight-line segments. Different LRalgorithms result from different choices on whether the left or right rule is applied at any node of T. We are interested in constructing LR-drawings (that are drawings obtained via LR-algorithms) with small width. Chan showed three LRalgorithms that achieve, for an n-node ordered rooted binary tree, width O(n0:695), width O(n0:5), and width O(n0:48). We prove that, for every n-node ordered rooted binary tree, an LR-drawing with minimum width can be constructed in O(n1:48) time. Further, we show an infi- nite family of n-node ordered rooted binary trees requiring (nO:418) width in any LR-drawing; no lower bound better than (log n) was previously known. Finally, we present the results of an experimental evaluation that allowed us to determine the minimum width of all the ordered rooted binary trees with up to 455 nodes. Our interest in LR-drawings is mainly motivated by a result of Di Battista and Frati [Algorithmica 2009], who proved that n-vertex outerplanar graphs have outerplanar straight-line drawings in O(n1:48) area by means of a drawing algorithm which resembles an LR-algorithm. We deepen the connection between LR-drawings and outerplanar drawings by proving that, if n-node ordered rooted binary trees have LR-drawings with f(n) width, for any function f(n), then n-vertex outerplanar graphs have outerplanar straight-line drawings in O(f(n)) area. Finally, we exploit a structural decomposition for ordered rooted binary trees introduced by Chan in order to prove that every n-vertex outerplanar graph has an outerplanar straight-line drawing in O (n 2 p 2 log2 np log n) area
Transcriptional responses of glutathione transferase genes in Ruditapes philippinarum exposed to microcystin-LR
No full textNo abstracts are to be cited without prior reference to the author. Microcystins (MCs) are potent hepatotoxins produced by bloom-forming species of toxic cyanobacteria. Among these, MC-LR is the most commonly found and toxic variant. Bivalves, due to their benthic and sedentary mode of life, are one of the most threatened organisms by these environmental stressors. Glutathione transferases (GSTs) play a major role in cellular defense against MCs toxicity. The aim of this study was to compare the relative changes of gene expression of the different GSTs isoforms in mollusc bivalves exposed to MCs. The time-dependent changes of relative transcription abundance of several GST isoforms in parallel with enzymatic activity of total GST were investigated in gills and hepatopancreas of Ruditapes philippinarum exposed to dissolved MC-LR. The relative changes of gene expression and enzyme activity were analyzed by quantitative real-time PCR and colorimetric assays respectively. We found that MC-LR could affect the transcriptional activities of these detoxification enzymes in gills and hepatopancreas of the tested bivalves. Most GST isoforms showed differential response profiles depending on the concentrations of MC-LR and exposure times for clams. These results highlight the important role of GSTs in counteracting the potential deleterious effects induced by MCs in bivalve
Fast removal of cyanobacterial toxin microcystin-LR by a low-cytotoxic microgel-Fe(III) complex
No full textEutrophication has become a serious environmental threat throughout the world. In particular, the presence of cyanobacteria toxins, especially microcystins (MCs), has become a severe problem. Inhibition of Microcystis growth in water resources is the most effective way to reduce MCs, but it is a long-term investment. In the present study, a microgel-Fe(III) complex was developed for the fast removal of MC-LR. The microgel-Fe(III) characteristics and the MC-LR removal dynamics in Milli-Q water and natural water were evaluated. The removal efficiency negatively correlated to the initial MC-LR concentration and pH value (2.0-11.5), but the kinetics was not significantly influenced. The presence of natural organic matter (NOM) in water slightly reduced MC-LR removal using microgel-Fe(III). In addition, microgel-Fe(III) removed 98.99% of MC-LR in 12 min, while for activated carbon, it took 15-24 h to reach equilibrium. Furthermore, methanol was found to regenerate the microgel-Fe(III) after MC-LR removal for at least five regeneration cycles. Finally, the microgel-Fe(III) material was made into a membrane so that MCs could be removed by filtration. Therefore, microgel-Fe(III) is an effective technology and has a great potential in removing MC-LR from drinking water resources. (C) 2011 Elsevier Ltd. All rights reserved.Eutrophication has become a serious environmental threat throughout the world. In particular, the presence of cyanobacteria toxins, especially microcystins (MCs), has become a severe problem. Inhibition of Microcystis growth in water resources is the most effective way to reduce MCs, but it is a long-term investment. In the present study, a microgel-Fe(III) complex was developed for the fast removal of MC-LR. The microgel-Fe(III) characteristics and the MC-LR removal dynamics in Milli-Q water and natural water were evaluated. The removal efficiency negatively correlated to the initial MC-LR concentration and pH value (2.0-11.5), but the kinetics was not significantly influenced. The presence of natural organic matter (NOM) in water slightly reduced MC-LR removal using microgel-Fe(III). In addition, microgel-Fe(III) removed 98.99% of MC-LR in 12 min, while for activated carbon, it took 15-24 h to reach equilibrium. Furthermore, methanol was found to regenerate the microgel-Fe(III) after MC-LR removal for at least five regeneration cycles. Finally, the microgel-Fe(III) material was made into a membrane so that MCs could be removed by filtration. Therefore, microgel-Fe(III) is an effective technology and has a great potential in removing MC-LR from drinking water resources. (C) 2011 Elsevier Ltd. All rights reserved
Incremental Scannerless Generalized LR Parsing
No full textThe Scannerless Generalized LR (SGLR) parsing algorithm supports the development of composed languages seamlessly but does not support incremental parsing. The Incremental Generalized LR (IGLR) parsing algorithm, on the other hand, does not support the seamless composition of languages. This thesis presents the Incremental Scannerless Generalized LR (ISGLR) parsing algorithm and investigates the effects of combining the SGLR and IGLR parsing algorithms. While the algorithmic differences are orthogonal, the fact that scannerless parsing relies on non-deterministic parsing for disambiguation has a negative impact on incrementality. Nonetheless, we show that the ISGLR parsing algorithm performs better than the batch SGLR parsing algorithm in typical scenarios. On average, the ISGLR parser can reuse 99% of a previous parse result. When parsing from scratch, the ISGLR parser has a 24% run time overhead compared to the SGLR parser, but when parsing incrementally for changes that are smaller than 1% of the input size on average, it has a 9× speedup.Successor of https://doi.org/10.1145/3359061.3361085Computer Scienc
TOXIC EFFECTS OF MICROCYSTIN-LR ON MICE ERYTHROCYTES in vitro
No full textHaematological abnormalities have been verified in patients intoxicated by microcystins (MCs) in haemodialysis unit in Caruaru, Brazil, and 60 patients died. In our previous studies, obvious anemia has been determined in rabbit after in vivo exposure to microcystins. As to the cause of the anemia, except for hematopoiesis obstacles, we hypothesized that microcystins result in erythrocyte destruction. In the present study, Kunming mice erythrocytes in vitro were incubated with 1, 10, 100 and 1000 nM microcystin-LR at 37 degrees C. Lipid peroxidation, haemolysis, cell morphology, antioxidative response and some biochemical biomarkers were measured. The results showed that the level of lipid peroxidation significantly increased in microcystin-LR treatment groups. The level of glutathione and activities of glutathione peroxidase, glutathione-S-transferase and superoxide dismutase were significantly increased after incubation with microcystin-LR at 12, 24 and 48 h. Also, significant decreases in activities of acetylcholinesterase, Na+-K+-ATPase and Ca2+-Mg2+-ATPase were observed. Obvious increases of haemolysis were determined in 10, 100 and 1000 nM groups from 12 to 48 h. Additionally, abnormal erythrocytes with bleb-bing and notched cell membrane were observed in both 100 and 1000 nM groups. It is presumed that microcystin-LR triggers lipid peroxidation of erythrocytes and oxidative stress destroys the structure of cell membrane, leading to alterations of antioxidative enzymes and biochemical indicators. Our results demonstrate that in vitro exposure to microcystin-LR resulted in damage of mice erythrocytes.Haematological abnormalities have been verified in patients intoxicated by microcystins (MCs) in haemodialysis unit in Caruaru, Brazil, and 60 patients died. In our previous studies, obvious anemia has been determined in rabbit after in vivo exposure to microcystins. As to the cause of the anemia, except for hematopoiesis obstacles, we hypothesized that microcystins result in erythrocyte destruction. In the present study, Kunming mice erythrocytes in vitro were incubated with 1, 10, 100 and 1000 nM microcystin-LR at 37 degrees C. Lipid peroxidation, haemolysis, cell morphology, antioxidative response and some biochemical biomarkers were measured. The results showed that the level of lipid peroxidation significantly increased in microcystin-LR treatment groups. The level of glutathione and activities of glutathione peroxidase, glutathione-S-transferase and superoxide dismutase were significantly increased after incubation with microcystin-LR at 12, 24 and 48 h. Also, significant decreases in activities of acetylcholinesterase, Na+-K+-ATPase and Ca2+-Mg2+-ATPase were observed. Obvious increases of haemolysis were determined in 10, 100 and 1000 nM groups from 12 to 48 h. Additionally, abnormal erythrocytes with bleb-bing and notched cell membrane were observed in both 100 and 1000 nM groups. It is presumed that microcystin-LR triggers lipid peroxidation of erythrocytes and oxidative stress destroys the structure of cell membrane, leading to alterations of antioxidative enzymes and biochemical indicators. Our results demonstrate that in vitro exposure to microcystin-LR resulted in damage of mice erythrocytes
Residue theorem and summing over Kaluza-Klein excitations
No full textApplying the equations of motion together with corresponding boundary conditions of bulk profiles at infrared and ultraviolet branes, we verify some lemmas on the eigenvalues of Kaluza-Klein modes in extension of the standard model with a warped extra dimension and the custodial symmetry SU(3)(c) X SU(2)(L) X SU(2)(R) X U(1)(X) X P-LR. Using the lemmas and performing properly analytic extensions of bulk profiles, we present the sufficient condition for a convergent series of Kaluza-Klein excitations and sum over the series through the residue theorem. The method can also be applied to sum over the infinite series of Kaluza-Klein excitations in a universal extra dimension. Furthermore, we analyze the possible connection between the propagators in five-dimensional full theory and the product of bulk profiles with corresponding propagators of exciting Kaluza-Klein modes in four-dimensional effective theory, and recover some relations presented in the literature for warped and universal extra dimensions, respectively. As an example, we present the correction from new physics to the branching ratio of (B) over bar -> X-s gamma to the order O(mu(2)(EW)/Lambda(2)(KK)) in extension of the standard model with a warped extra dimension and the custodial symmetry, where Lambda(KK) denotes the energy scale of low-lying Kaluza-Klein excitations and mu(EW) denotes the electroweak energy scale.Astronomy & AstrophysicsPhysics, Particles & FieldsSCI(E)0ARTICLE9null8
Construction Methods of LR Parsers
No full textThis paper presents five different LR parser generators and an error recovery method which is derived directly from the LR parser. The parsers presented include the original LR (1) parser defined by Knuth. The SLR(1) and LALR(1) parsers defined by DeRemer, and the weak and strong compatible LR parsers presented by Pager. All five parsers have been implemented by the author using two programs. Furthermore, the implementation of the SLR (1) parser generator includes an error recovery method and produces an SLR(1) parser with error recovery built in
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