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Poly(neutral red) based hydrogen peroxide biosensor for chromium determination by inhibition measurements

Attar, Aisha; Ghica, M. Emilia; Amine, Aziz; Brett, Christopher M. A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
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Amperometric hydrogen peroxide enzyme inhibition biosensors based on horseradish peroxidase (HRP) immobilised on electropolymerised neutral red (NR) or directly on the surface of carbon film electrodes (CFE) have been successfully applied to the determination of toxic Cr(III) and Cr(VI). Parameters influencing the performance of the biosensor including the enzyme immobilisation method, the amount of hydrogen peroxide, applied potential and electrolyte pH were optimised. The inhibition of horseradish peroxidase by the chromium species was studied under the optimised conditions. Results from the quantitative analysis of chromium ions are discussed in terms of detection limit, linear range and sensitivity. The HRP kinetic interactions reveal mixed binding of Cr(III) with I50 = 3.8 μM and inhibition binding constant Ki = 11.3 μM at HRP/PNR/CFE biosensors and uncompetitive binding of Cr(VI) with I50 = 3.9 μM and Ki = 0.78 μM at HRP/CFE biosensors in the presence of H2O2 substrate. Interferences from other heavy metal ions were studied and the inhibition show very good selectivity towards Cr(III) and Cr(VI).

PKC beta II inhibition attenuates myocardial infarction induced heart failure and is associated with a reduction of fibrosis and pro-inflammatory responses

Palaniyandi, Suresh Selvaraj; Ferreira, Julio Cesar Batista; Brum, Patricia Chakur; Mochly-Rosen, Daria
Fonte: WILEY-BLACKWELL Publicador: WILEY-BLACKWELL
Tipo: Artigo de Revista Científica
ENG
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36.07%
Protein kinase C beta II (PKC beta II) levels increase in the myocardium of patients with end-stage heart failure (HF). Also targeted overexpression of PKC beta II in the myocardium of mice leads to dilated cardiomyopathy associated with inflammation, fibrosis and myocardial dysfunction. These reports suggest a deleterious role of PKC beta II in HF development. Using a post-myocardial infarction (MI) model of HF in rats, we determined the benefit of chronic inhibition of PKC beta II on the progression of HF over a period of 6 weeks after the onset of symptoms and the cellular basis for these effects. Four weeks after MI, rats with HF signs that were treated for 6 weeks with the PKC beta II selective inhibitor (beta IIV5-3 conjugated to TAT(47-57) carrier peptide) (3 mg/kg/day) showed improved fractional shortening (from 21% to 35%) compared to control (TAT(47-57) carrier peptide alone). Formalin-fixed mid-ventricle tissue sections stained with picrosirius red, haematoxylin and eosin and toluidine blue dyes exhibited a 150% decrease in collagen deposition, a two-fold decrease in inflammation and a 30% reduction in mast cell degranulation, respectively, in rat hearts treated with the selective PKC beta II inhibitor. Further, a 90% decrease in active TGF beta 1 and a significant reduction in SMAD2/3 phosphorylation indicated that the selective inhibition of PKC beta II attenuates cardiac remodelling mediated by the TGF-SMAD signalling pathway. Therefore...

Effects of microinjections of apomorphine and haloperidol into the inferior colliculus on the latent inhibition of the conditioned emotional response

MELO, Liana L.; PEREIRA, Ellen C. H. M.; PAGINI, Cassia H.; COIMBRA, Norberto C.; BRANDAO, Marcus L.; FERRARI, Elenice A. M.
Fonte: ACADEMIC PRESS INC ELSEVIER SCIENCE Publicador: ACADEMIC PRESS INC ELSEVIER SCIENCE
Tipo: Artigo de Revista Científica
ENG
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36.07%
Electrical or chemical stimulation of the inferior colliculus (IC) induces fear-like behaviors. More recently, consistent evidence has shown that electrical stimulation of the central nucleus of the IC supports Pavlovian conditioning and latent inhibition (Li). LI is characterized by retardation in conditioning and also by an impaired ability to ignore irrelevant stimuli, after a non-reinforced pre-exposure to the conditioned stimulus. LI has been proposed as a behavioral model of cognitive abnormalities seen in schizophrenia. The aim of the present study was to determine whether dopaminergic mechanisms in the IC are involved in LI of the conditioned emotional response (CER). To induce LI, a group of rats was pre-exposed (PE) to six tones in two sessions, while rats that were not pre-exposed (NPE) had two sessions without tone presentations. The conditioning consisted of two tone presentations to the animal, followed immediately by a foot shock. PE and NPE rats received IC microinjections of physiological saline, the dopaminergic agonist apomorphine (9.0 mu g/0.5 mu L/side), or the dopaminergic antagonist haloperidol (0.5 mu g/0.5 mu L/side) before both pre-exposure and conditioning. During the test, the PE rats that received saline or haloperidol had a lower suppression of the licking response compared to NPE rats that received vehicle or haloperidol...

Inhibition of human platelet aggregation by eosinophils

Maziero, Aline Mendes; Lorenzetti, Raquel; Donato, José Luiz; Lilla, Sergio; Nucci, Gilberto de
Fonte: Pergamon Press; Oxford Publicador: Pergamon Press; Oxford
Tipo: Artigo de Revista Científica
ENG
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36.09%
AIMS: The relationship between the activity of eosinophils and platelets has been observed in recent decades by many scientists. These observations include increased numbers of eosinophils associated with platelet disorders, including changes in the coagulation cascade and platelet aggregation. Based on these observations, the interaction between eosinophils and platelets in platelet aggregation was analyze. MAIN METHODS: Human platelets were incubated with eosinophil cytosolic fraction, promyelocytic human HL-60 clone 15 cell lineage, and eosinophil cationic protein (ECP). Platelet rich plasma (PRP) aggregation was induced by adenosine diphosphate, platelet activating factor, arachidonic acid, and collagen, and washed platelets (WP) were activated by thrombin. KEY FINDINGS: Aggregation induced by all agonists was dose dependently inhibited by eosinophil cytosolic fraction. This inhibition was only partially reversed by previous incubation of the eosinophils with l-Nitro-Arginine-Methyl-Ester (l-NAME). Previous incubation with indomethacin did not prevent the cytosolic fraction induced inhibition. The separation of eosinophil cytosolic fraction by gel filtration on Sephadex G-75 showed that the inhibitory activity was concentrated in the lower molecular weight fraction. HL-60 clone 15 cells differentiated into eosinophils for 5 and 7 day were able to inhibit platelet aggregation. The ECP protein inhibited the platelet aggregation on PRP and WP. This inhibition was more evident in WP...

Inhibition of cysteine proteases by a natural biflavone: behavioral evaluation of fukugetin as papain and cruzain inhibitor

Assis, Diego Magno; Gontijo, Vanessa Silva; Pereira, Ivan de Oliveira; Santos, Jorge Alexandre Nogueira; Camps, Ihosvany; Nagem, Tanus Jorge; Ellena, Javier; Izidoro, Mario Augusto; Tersariol, Ivarne Luis dos Santos; Barros, Nilana Meza Tenório de; Dorig
Fonte: Informa Healthcare; London Publicador: Informa Healthcare; London
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.09%
Cruzain is the major cysteine protease of Trypanosoma cruzi, the infectious agent responsible for Chagas disease, and cruzain inhibitors display considerable antitrypanosomal activity. In the present work we elucidated crystallographic data of fukugetin, a biflavone isolated from Garcinia brasiliensis, and investigated the role of this molecule as cysteine protease inhibitor. The kinetic analyses demonstrated that fukugetin inhibited cruzain and papain by a slow reversible type inhibition with KI of 1.1 and 13.4 μM, respectively. However, cruzain inhibition was about 12 times faster than papain inhibition. Lineweaver-Burk plots demonstrated partial competitive inhibition for cruzain and hyperbolic mixed-type inhibition for papain. Furthermore, the docking results showed that the biflavone binds to ring C′ in the S2 pocket and to ring C in the S3 pocket through hydrophobic interactions and hydrogen bonds. Finally, fukugetin also presented inhibitory activity on proteases of the T. cruzi extract, with IC50 of 7 μM.; FAPEMIG (APQ-01420-08); FAPESP (08/54894-4); CNPq

The relationship between inhibition of bacterial adhesion to a solid surface by sub-MICs of antibiotics and subsequent development of a biofilm

Cerca, Nuno; Martins, Silvia; Pier, Gerald B.; Oliveira, Rosário; Azeredo, Joana
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2005 ENG
Relevância na Pesquisa
36.09%
Many studies have demonstrated that subminimal inhibitory concentrations (sub-MICs) of antibiotics can inhibit initial microbial adherence to medical device surfaces. It has been suggested that, by inhibiting initial adhesion, biofilm formation might be prevented. However, since initial adherence and subsequent biofilm formation may be two distinct phenomena, conclusions regarding the effects of sub-MIC antibiotics on initial adhesion cannot be extrapolated to biofilm formation. In this study, we evaluated the adherence of several clinical isolates of coagulase-negative staphylococci (CoNS) to acrylic and the effect of sub-MICs of vancomycin, cefazolin, dicloxacillin and combinations of these antibiotics on adherence and biofilm formation. Most of the antibiotics used resulted in effective reduction of bacterial adherence to acrylic, in some cases reaching over 70% inhibition of adherence. When strains with a high biofilm-forming capacity were grown in sub-MICs of those antibiotics, there existed combinations of the drugs that significantly inhibited biofilm formation. However, most of the antibiotic combinations that inhibited adherence did not have a profound effect on biofilm formation. When comparing the results of the effect of sub-MIC amounts of antibiotics in inhibiting adherence with their effect on the inhibition of biofilm formation...

Determination of inhibition in the enzymatic hydrolysis of cellobiose using hybrid neural modeling

Corazza,F. C.; Calsavara,L. P. V.; Moraes,F. F.; Zanin,G. M.; Neitzel,I.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2005 EN
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36.16%
Neural networks and hybrid models were used to study substrate and product inhibition observed in the enzymatic hydrolysis of cellobiose at 40ºC, 50ºC and 55ºC, pH 4.8, using cellobiose solutions with or without the addition of exogenous glucose. Firstly, the initial velocity method and nonlinear fitting with StatisticaÒ were used to determine the kinetic parameters for either the uncompetitive or the competitive substrate inhibition model at a negligible product concentration and cellobiose from 0.4 to 2.0 g/L. Secondly, for six different models of substrate and product inhibitions and data for low to high cellobiose conversions in a batch reactor, neural networks were used for fitting the product inhibition parameter to the mass balance equations derived for each model. The two models found to be best were: 1) noncompetitive inhibition by substrate and competitive by product and 2) uncompetitive inhibition by substrate and competitive by product; however, these models’ correlation coefficients were quite close. To distinguish between them, hybrid models consisting of neural networks and first principle equations were used to select the best inhibition model based on the smallest norm observed, and the model with noncompetitive inhibition by substrate and competitive inhibition by product was shown to be the best predictor of cellobiose hydrolysis reactor behavior.

Behaviorial inhibition and history of childhood anxiety disorders in Brazilian adult patients with panic disorder and social anxiety disorder

Isolan,Luciano Rassier; Zeni,Cristian Patrick; Mezzomo,Kelin; Blaya,Carolina; Kipper,Leticia; Heldt,Elizeth; Manfro,Gisele Gus
Fonte: Associação Brasileira de Psiquiatria - ABP Publicador: Associação Brasileira de Psiquiatria - ABP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2005 EN
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PURPOSE: To evaluate the presence of behavioral inhibition and anxiety disorders during childhood in Brazilian adult patients with panic disorder and social anxiety disorder compared to a control group. METHODS: Fifty patients with panic disorder, 50 patients with social anxiety disorder, and 50 control subjects were included in the study. To assess the history of childhood anxiety, the Schedule for Affective Disorders and Schizophrenia for School Age Children, Epidemiologic Version (K-SADS-E), and the Diagnostic Interview for Children and Adolescents-Parent Version (DICA-P) were used. The presence of behavioral inhibition in childhood was assessed by the self-reported scale of Behavioral Inhibition Retrospective Version (RSRI-30). RESULTS: Patients showed significantly higher prevalence of anxiety disorders and behavioral inhibition in childhood compared to the control group. Patients with social anxiety disorder also showed significantly higher rates of avoidance disorder (46% vs. 18%, p = 0.005), social anxiety disorder (60% vs. 26%, p = 0.001), presence of at least one anxiety disorder (82% vs. 56%, p = 0.009) and global behavioral inhibition (2.89 ± 0.61 vs. 2.46 ± 0.61, p < 0.05) and school/social behavioral inhibition (3.56 ± 0.91 vs. 2.67 ± 0.82...

Dissociable Recruitment of Rostral Anterior Cingulate and Inferior Frontal Cortex in Emotional Response Inhibition

Holmes, Avram; Pizzagalli, Diego; Chiu, Pearl H.
Fonte: Academic Press Publicador: Academic Press
EN_US
Relevância na Pesquisa
36.13%
The integrity of decision-making under emotionally evocative circumstances is critical to navigating complex environments, and dysfunctions in these processes may play an important role in the emergence and maintenance of various psychopathologies. The goal of the present study was to examine the spatial and temporal dynamics of neural responses to emotional stimuli and emotion-modulated response inhibition. High-density event-related brain potentials (ERPs) were measured as participants (N=25) performed an emotional Go/NoGo task that required button presses to words of a "target" emotional valence (i.e., positive, negative, neutral) and response inhibition to words of a different "distractor" valence. Using scalp ERP analyses in conjunction with source-localization techniques, we identified distinct neural responses associated with affective salience and affect- modulated response inhibition, respectively. Both earlier (similar to 300 ms) and later (similar to 700 ms) ERP components were enhanced with successful response inhibition to emotional distractors. Only ERPs to target stimuli differentiated affective from neutral cues. Moreover, Source localization analyses revealed right ventral lateral prefrontal cortex (VLPFC) activation in affective response inhibition regardless of emotional valence...

Continuity and discontinuity in behavioral inhibition : influences of a maltreating environment

Holmes, Beth Cerrito (1977 - ); Rogosch, Fred A.
Fonte: University of Rochester. Publicador: University of Rochester.
Tipo: Tese de Doutorado Formato: Number of Pages:xii, 165 leaves
ENG
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Thesis (Ph. D.)--University of Rochester. Dept. of Clinical and Social Sciences in Psychology, 2008.; Behavioral inhibition is one of the most frequently studied traits of child temperament. Although consistent with theoretical views of temperament, the biological and physiological underpinnings of behavioral inhibition have often been highlighted to the exclusion or minimization of environmental factors. Nevertheless, a growing literature suggests that environment plays a role in the development and expression of temperamental traits. Further, given a developmental psychopathology framework, the processes of normal development can be elucidated by the examination of maladaptive or otherwise atypical developmental patterns or environments (Cicchetti, 1984; 1990; Sroufe, 1990). The current study addresses the above issues in two ways – by examining the rates and stability of traditional behavioral inhibition across the second year of life in children from maltreating and nonmaltreating families and by proposing an alternate method of classifying behavioral inhibition for possible greater precision in non-normative, higher-risk samples. Behavioral inhibition was assessed through a standard laboratory paradigm when children were 14 and 26-months of age. Trained raters coded data for both fear behaviors (i.e....

Kinetics and inhibition of the formation of 6β-naltrexol from naltrexone in human liver cytosol; Kinetics and inhibition of the formation of 6beta-naltrexol from naltrexone in human liver cytosol

Porter, S.; Somogyi, A.; White, J.
Fonte: Blackwell Science Ltd Publicador: Blackwell Science Ltd
Tipo: Artigo de Revista Científica
Publicado em //2000 EN
Relevância na Pesquisa
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Aims: To determine the kinetics of the formation of 6β-naltrexol from naltrexone in human liver cytosol, and to investigate the role of potential inhibitors. Methods: The kinetics of the formation of 6β-naltrexol from naltrexone were examined in eight human liver cytosol preparations using h.p.l.c. to quantify 6β-naltrexol and, the extent of inhibition of 6β-naltrexol formation was determined using chemical inhibitors. The formation of 6β-naltrexol and the back reaction of 6β-naltrexol to naltrexone were also examined in a microsomal preparation. Results: The Vmax, Km and CLint values for the formation of 6β-naltrexol from naltrexone were in the ranges of 16–45 nmol mg−1 protein h−1, 17–53 µm and 0.3–2.2 ml h−1 mg−1 protein, respectively. The steroid hormones testosterone (Ki = 0.3 ± 0.1 µm) and dihydrotestosterone (Ki = 0.7 ± 0.4 µm) were the most potent competitive inhibitors of 6β-naltrexol formation, with naloxone, menadione and corticosterone also producing > 50% inhibition at a concentration of 100 µm. The opioid agonists morphine, oxycodone, oxymorphone and hydromorphone, and a range of benzodiazepines showed < 20% inhibition at 100 µm. In the microsomal preparation, there was no formation of naltrexone from 6β-naltrexol nor any formation of 6β-naltrexol from naltrexone. Conclusions: The intersubject variability in the kinetic parameters of 6β-naltrexol formation could play a role in the efficacy of and patient compliance with naltrexone treatment. This variability could be due in part to a genetic polymorphism of the dihydrodiol dehydrogenase DD4...

Beyond Endophenotypes: Direct and Indirect Effects of Sustained Attention and Behavioral Inhibition on Attention Deficit Hyperactivity Disorder

Reinelt, Tilman
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertação
EN
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36.11%
Current theoretical accounts investigating the etiology of Attention Deficit Hyperactivity Disorder (ADHD) rely on cognitive or motivational deficits, neuronal impairments, and genetic predispositions. Relying on the endophenotype concept, this thesis provides a theoretical framework to integrate these lines of research. The framework moves beyond a mere endophenotype approach as both direct effects of cognitive and motivational functions on ADHD symptoms and indirect effects of cognitive or motivational functions on ADHD symptoms through higher-order psychological functions are considered. Both, sustained attention and behavioral inhibition, are related to risky decision-making and risky decision- making in turn is associated with impulsivity and ADHD symptoms. Hence, this thesis addresses the question whether indirect effects through risky decision-making can account for relations between sustained attention, behavioral inhibition, and ADHD symptoms. Method. Ninety-five children (71 males; 40 children with a diagnosed ADHD) aged between 7;4 and 13;8 years met inclusion criteria for the current study. Children worked on three computerized cognitive tasks measuring sustained attention and behavioral inhibition as well as three behavioral tasks measuring risky decision-making. Results. A sustained attention composite score significantly predicted ADHD symptoms...

Let’s Go or Not Go! Behavioral Investigation of the Effect of Methylphenidate on Response Inhibition in Children with Attention Deficit Hyperactivity Disorder

Hung, Shuan-Ju
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertation; info:eu-repo/semantics/doctoralThesis
EN
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The core symptoms of children with attention deficit hyperactivity disorder (ADHD) are inattention, hyperactivity, and impulsivity (American Psychiatric Association, 2000). A primary deficit in inhibitory control is proposed to account for dysfunctional behavior patterns associated with this disorder (Barkley, 1997). Early research has shown that medication (e.g., Methylphenidate) is effective when it comes to enhancing inhibitory control (e.g., Pliszka et al., 2007). Therefore, by incorporating relevant results from the previous study (Paul-Jordanov, Bechtold, & Gawrilow, 2010) , we explored the effect of medication on inhibition in children with ADHD in Germany and Taiwan at the same time. Children with ADHD and normally developing children in Germany and Taiwan were recruited for the current studies. In Study 1, using a Go/NoGo task, we investigated the response inhibition of children with ADHD and their healthy counterparts at both sites. Significantly, children with ADHD in Germany showed deficits in response inhibition compared to their healthy counterparts. A group difference, however, was not pronouncedly observed in the Taiwanese sample. In Study 2, the effect of medication on response inhibition was explored in children with ADHD. After the treatment of medication...

Co-Inhibition von epidermal growth factor receptor (EGFR) und insulin-like growth factor-I receptor (IGF-IR): Ein neuer Ansatz für die Reduktion der Zelltodresistenz humaner maligner Gliomzellen; Co-inhibition of epidermal growth factor receptor and type 1 insulin-like growth factor receptor: a new approach in reducing of restistance to apoptosis of human malignant glioma cells

Eisenmann, Christine
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertation; info:eu-repo/semantics/doctoralThesis
DE_DE
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36.19%
In der vorliegenden Arbeit wurde zunächst der Effekt der Wachstumsfaktoren EGF, IGF-I, FGF-I und PDGF auf Wachstum und Überleben von zwölf humanen malignen Glioblastomzellinien bei Serumentzug untersucht. Dabei wurden bei den einzelnen Zelllinien unterschiedliche Abhängigkeit von individuellen Wachstumsfaktoren beobachtet, die als eine Art 'molekulare Signatur' Hinweise auf die Relevanz der zugehörigen Rezeptortyrosinkinase gelten können. Die Charakterisierung der Effekte einer Co-Inhibition von EGFR und IGF-IR auf den CD95L-induzierten Zelltod war der zentrale Bestandteil dieser Arbeit. Dabei konnte zunächst eine synergistische Sensitivierung gegenüber CD95 durch die Co-Inhibition bei den p53-Wildtyp-Zelllinien LNT-229 und U87MG nachgewiesen werden, nicht jedoch bei den p53-mutanten Zelllinien LN-18 und T98G. Experimente mit dem temperatursensitiven p53val135A zeigten jedoch, dass der sensitivierende Effekt der Co-Inhibition nicht p53-abhängig ist. Der Typ des durch die Co-Inhibition fazilitierten Zelltods war apoptotisch und begleitet von einer crmA-sensitiven Aktivierung von Caspase 8, den Effektorcaspasen 3 und 7, und dem Caspasesubstrat PARP. Da ein Effekt der Co-Inhibition auf das Expressionsniveau von CD95 ausgeschlossen wurde...

Local and large-range inhibition in feature detection

Bolzon, D.; Nordstrom, K.; O'Carroll, D.
Fonte: Soc Neuroscience Publicador: Soc Neuroscience
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
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36.09%
Lateral inhibition is perhaps the most ubiquitous of neuronal mechanisms, having been demonstrated in early stages of processing in many different sensory pathways of both mammals and invertebrates. Recent work challenges the long-standing view that assumes that similar mechanisms operate to tune neuronal responses to higher order properties. Scant evidence for lateral inhibition exists beyond the level of the most peripheral stages of visual processing, leading to suggestions that many features of the tuning of higher order visual neurons can be accounted for by the receptive field and other intrinsic coding properties of visual neurons. Using insect target neurons as a model, we present unequivocal evidence that feature tuning is shaped not by intrinsic properties but by potent spatial lateral inhibition operating well beyond the first stages of visual processing. In addition, we present evidence for a second form of higher-order spatial inhibition—a long-range interocular transfer of information that we argue serves a role in establishing interocular rivalry and thus potentially a neural substrate for directing attention to single targets in the presence of distracters. In so doing, we demonstrate not just one, but two levels of spatial inhibition acting beyond the level of peripheral processing.; Douglas M. Bolzon...

Linear competitive inhibition of human tissue kallikrein by 4-aminobenzamidine and benzamidine and linear mixed inhibition by 4-nitroaniline and aniline

Sousa,M.O.; Miranda,T.L.S.; Costa,E.B.; Bittar,E.R.; Santoro,M.M.; Figueiredo,A.F.S.
Fonte: Associação Brasileira de Divulgação Científica Publicador: Associação Brasileira de Divulgação Científica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2001 EN
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36.09%
Hydrolysis of D-valyl-L-leucyl-L-arginine p-nitroanilide (7.5-90.0 µM) by human tissue kallikrein (hK1) (4.58-5.27 nM) at pH 9.0 and 37ºC was studied in the absence and in the presence of increasing concentrations of 4-aminobenzamidine (96-576 µM), benzamidine (1.27-7.62 mM), 4-nitroaniline (16.5-66 µM) and aniline (20-50 mM). The kinetic parameters determined in the absence of inhibitors were: Km = 12.0 ± 0.8 µM and k cat = 48.4 ± 1.0 min-1. The data indicate that the inhibition of hK1 by 4-aminobenzamidine and benzamidine is linear competitive, while the inhibition by 4-nitroaniline and aniline is linear mixed, with the inhibitor being able to bind both to the free enzyme with a dissociation constant Ki yielding an EI complex, and to the ES complex with a dissociation constant Ki', yielding an ESI complex. The calculated Ki values for 4-aminobenzamidine, benzamidine, 4-nitroaniline and aniline were 146 ± 10, 1,098 ± 91, 38.6 ± 5.2 and 37,340 ± 5,400 µM, respectively. The calculated Ki' values for 4-nitroaniline and aniline were 289.3 ± 92.8 and 310,500 ± 38,600 µM, respectively. The fact that Ki'>Ki indicates that 4-nitroaniline and aniline bind to a second binding site in the enzyme with lower affinity than they bind to the active site. The data about the inhibition of hK1 by 4-aminobenzamidine and benzamidine help to explain previous observations that esters...

Feeding inhibition in the soil collembolan Folsomia candida as an endpoint for the estimation of organic waste ecotoxicity

Domene, X.; Alcañiz, Josep M.; Andrés, Pilar; Natal-Da-Luz, Tiago; Sousa, José Paulo
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/acceptedVersion Formato: application/pdf
Publicado em //2007 ENG
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Despite the increasing quantities of organic wastes that are being reused in soils, there are few studies that focus on the selection of bioassays for the ecotoxicological risk assessment of organic wastes to soils. In the present study, differences in feeding inhibition in the soil collembolan Folsomia candida were evaluated as an ecotoxicological endpoint for the assessment of risk to soils amended with polluted organic wastes. Seven organic wastes (dewatered sewage sludges, thermally dried sewage sludges, composted sewage sludges, and a thermally dried pig slurry) were tested. These wastes had different origins, treatments, and pollutant burdens, and were selected as a representative sample of the wide variety of wastes currently generated. A clear dose response was observed for this parameter, with an increase in percentage of individual feeding inhibition with increased doses of organic wastes. More significantly, feeding inhibition correlated highly with mortality and reproduction inhibition in the different wastes. Composted sludges displayed the lowest toxicity, followed by thermally dried sludge and dewatered sludge. Thermally dried pig slurry showed the highest toxicity for feeding, with lower median effective concentration (EC50) values than the lowest dose tested. Among waste physicochemical parameters and pollutants...

The relationship between side reactions and slow inhibition of ribulose-biphosphate carboxylase revealed by a loop 6 mutant of the tobacco enzyme

Pearce, Grant; Andrews, Thomas
Fonte: American Society for Biochemistry and Molecular Biology Inc Publicador: American Society for Biochemistry and Molecular Biology Inc
Tipo: Artigo de Revista Científica
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The first directed mutant of a higher plant ribulose-bisphosphate carboxylase/oxygenase (Rubisco), constructed by chloroplast transformation, is catalytically impaired but still able to support the plant's photosynthesis and growth (Whitney, S. M., von Caemmerer, S., Hudson, G. S., and Andrews, T. J. (1999) Plant Physiol. 121, 579-588). This mutant enzyme has a Leu to Val substitution at residue 335 in the flexible loop 6 of the large subunit, which closes over the substrate during catalysis. Its active site was intact, as judged by its barely impaired competency in the initial enolization step of the reaction sequence, and its ability to bind tightly the intermediate analog, 2′-carboxy-D-arabinitol-1,5-bisphosphate. Prompted by observations that the mutant enzyme displayed much less slow inhibition during catalysis in vitro than the wild type, its tendency to catalyze side reactions and its response to the slow inhibitor D-xylulose-1,5-bisphosphate were studied. The lessening in slow inhibition was not caused by reduced production of inhibitory side products. Except for pyruvate production, these reactions were strongly enhanced by the mutation, as was the ability to catalyze the carboxylation of D-xylulose-1,5-bisphosphate. Rather...

Regulation of skeletal ryanodine receptors by dihydropyridine receptor II-III loop C-region peptides: relief of Mg2+ inhibition

Haarmann, Claudia; Dulhunty, Angela; Laver, Derek Rowland
Fonte: Portland Press Publicador: Portland Press
Tipo: Artigo de Revista Científica
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36.11%
The aim of the present study was to explore interactions between surface-membrane DHPR (dihydropyridine receptor) Ca2+ channels and RyR (ryanodine receptor) Ca2+ channels in skeletal-muscle sarcoplasmic reticulum. The C region (725Phe-Pro742) of the linker between the 2nd and 3rd repeats (II-III loop) of the α1 subunit of skeletal DHPRs is essential for skeletal excitation-contraction coupling, which requires a physical interaction between the DHPR and RyR and is independent of external Ca2+. Little is known about the regulatory processes that might take place when the two Ca 2+ channels interact. Indeed, interactions between C fragments of the DHPR (C peptides) and RyR have different reported effects on Ca2+ release from the sarcoplasmic reticulum and on RyR channels in lipid bilayers. To gain insight into functional interactions between the proteins and to explore different reported effects, we examined the actions of C peptides on RyR1 channels in lipid bilayers with three key RyR regulators, Ca2+, Mg2+ and ATP. We identified four discrete actions: two novel, low-affinity (> 10 μM), rapidly reversible effects (fast inhibition and decreased sensitivity to Mg2+ inhibition) and two slowly reversible effects (high-affinity activation and a slow-onset...

Effect of Iodide Ions on Corrosion Inhibition of Mild Steel in 0.5 M H2SO4 by Poly(4-Vinylpyridine)

Larabi,Lahcène; Harek,Yahia
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2004 FR
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The effect of iodide ions on the corrosion inhibition of mild steel in 0.5 M sulfuric acid in the presence of poly(4-vinylpyridine) (p4vp) was studied by weight loss and different electrochemical techniques such as electrochemical impedance spectroscopy, potentiodynamic polarization and polarization resistance measurements. The obtained results showed that poly(4-vinylpyridine) effectively reduces the corrosion rate of mild steel. The addition of potassium iodide (KI) enhanced the inhibition efficiency (P%). The synergism parameter (Sp) calculated from inhibition efficiency was found to be greater than unity, suggesting that the phenomenon of synergism exists between P4VP and iodide ions. The adsorption of p4vp alone and in combination with KI followed Frumkin adsorption isotherm. The effect of temperature indicated that the inhibition efficiency of p4vp decreases with increasing temperature. Study of temperature effect showed also that inhibition efficiency of (P4VP + KI) does not depend on temperature. The apparent activation energies in the absence and in the presence of P4Vp and ( P4VP + KI ) were determined.