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‣ Efeito do tipo de corte e sanificantes no amaciamento de pequi (Caryocar brasiliense Camb.) minimamente processado

Rodrigues,Luiz José; Vilas Boas,Eduardo Valério de Barros; Piccoli,Roberta Hilsdorf; Paula,Nélio Ranieli Ferreira de; Pinto,Daniella Moreira; Vilas Boas,Brígida Monteiro
Fonte: Editora da Universidade Federal de Lavras Publicador: Editora da Universidade Federal de Lavras
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2007 Português
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Frutos e hortaliças minimamente processados devem apresentar atributos de conveniência e qualidade do produto fresco. Com o presente trabalho, objetivou-se avaliar a influência dos sanificantes hipoclorito de sódio (NaClO) 50 ppm e 100 ppm e peróxido de hidrogênio (H2O2) 4% e 6%, sobre os processos envolvidos no amaciamento de pequi (Caryocar brasiliense Camb.) minimamente processado submetido a dois tipos de processamento: "caroço fatiado" e "caroço inteiro" e armazenado a 6 ± 1ºC e 90% a 95% UR, durante 15 dias. A cada três dias foram avaliados: perda de massa, firmeza, pectina total, pectina solúvel, atividade de pectinametilesterase (PME) e atividade de poligalacturonase (PG). O pequi minimamente processado apresentou perda de massa e decréscimo de firmeza ao longo do período de armazenamento, concomitante ao aumento da atividade da enzima poligalacturonase, bem como solubilização de substâncias pécticas. Não foi verificada atividade de PME no pequi minimamente processado avaliado. Os caroços fatiados apresentaram maior teor de pectina solúvel, do 3° ao 6° dia e atividade da enzima poligalacturonase, do 3° ao 12° dia de armazenamento, em relação aos caroços inteiros. A sanificação com NaClO 50 ppm e 100 ppm...

‣ Models for the analysis of growth curves for rearing tinamous (Rhynchotus rufescens) in captivity

Tholon,P; Queiroz,SA
Fonte: Fundação APINCO de Ciência e Tecnologia Avícolas Publicador: Fundação APINCO de Ciência e Tecnologia Avícolas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2007 Português
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Growth curves models provide a visual assessment of growth as a function of time, and prediction body weight at a specific age. This study aimed at estimating tinamous growth curve using different models, and at verifying their goodness of fit. A total number 11,639 weight records from 411 birds, being 6,671 from females and 3,095 from males, was analyzed. The highest estimates of a parameter were obtained using Brody (BD), von Bertalanffy (VB), Gompertz (GP,) and Logistic function (LG). Adult females were 5.7% heavier than males. The highest estimates of b parameter were obtained in the LG, GP, BD, and VB models. The estimated k parameter values in decreasing order were obtained in LG, GP, VB, and BD models. The correlation between the parameters a and k showed heavier birds are less precocious than the lighter. The estimates of intercept, linear regression coefficient, quadratic regression coefficient, and differences between quadratic coefficient of functions and estimated ties of quadratic-quadratic-quadratic segmented polynomials (QQQSP) were: 31.1732±2.41339; 3.07898± 0.13287; 0.02689±0.00152; -0.05566±0.00193; 0.02349±0.00107, and 57 and 145 days, respectively. The estimated predicted mean error values (PME) of VB, GP, BD...

‣ Abundance and diversity patterns of the sessile macrobenthic community associated with environmental gradients in Vitória Harbor, southeastern Brazil

Zalmon,Ilana Rosental; Krohling,Werther; Ferreira,Carlos Eduardo Leite
Fonte: Sociedade Brasileira de Zoologia Publicador: Sociedade Brasileira de Zoologia
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2011 Português
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Harbor terminals and urban sewage effluents affect the composition and distribution of epibenthic organisms. In this study, we hypothesized that the benthic community structure at the Vitoria Harbor changes spatially in a ~3 km scale, and that these changes are associated with environmental gradients resulting from point-source sewage and differences in the physical and chemical parameters of the water along the harbor access channel. Four sites, internal (PI), intermediate-internal (PMI), intermediate-external (PME) and external (PE), varying from 0.5 to 4.0 km off the harbor, were sampled on five quadrats at six sampling dates (N = 30 per site). The epibenthic community on the shallow sublitoral rocky shore was sampled fortnightly from December 2005 to February 2006 by point-intersection method. A total of 27 taxa were registered with higher richness and diversity values at the external sites. The similarity analysis indicated two distinct systems, with the internal sites PI and PMI apart from the external PME and PE, which showed 97% of dissimilarity. While the internal sites presented some estuarine characteristics and a high coverage (> 60%) of hydrozoans and bryozoans with silt/clay, the external ones showed coastal water influence and higher amounts of sedimentary material substrate (> 50%). This pattern reflects the estuarine gradient and the suspended sedimentary material at the internal sites...

‣ Estimating Software Development Costs for a Patient Multimedia Education Project

Caban, Arlene; Cimino, Christopher; Swencionis, Charles; Ginsberg, Mindy; Wylie-Rosett, Judith
Fonte: American Medical Informatics Association Publicador: American Medical Informatics Association
Tipo: Artigo de Revista Científica
Publicado em //2001 Português
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The authors compare alternative methods of cost estimation for a patient multimedia education (PME) program, using a computerized weight-reduction PME project as an example. Data from the project planning and budgeting process and actual costs of the completed project are analyzed retrospectively to calculate three different estimates—pre-work, post-work, and actual work. Three traditional methods of estimating the cost of computer programs (the lines-of-code, function point, and task ratio analyses) underestimate costs in this example. A commercial program (Cost Xpert) that calculates the cost of developing a graphical user interface provided a better estimate, as did a tally reflecting the complexity and quality of media material in the project.

‣ Evaluation of Nucleoside Phosphonates and Their Analogs and Prodrugs for Inhibition of Orthopoxvirus Replication

Keith, Kathy A.; Hitchcock, Michael J. M.; Lee, William A.; Holý, Antonin; Kern, Earl R.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /07/2003 Português
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In the event of a bioterrorism attack using smallpox virus, there currently is no approved drug for the treatment of infections with this virus. We have reported previously that (S)-1-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine (HPMPC) (also known as cidofovir [CDV]) has good activity against poxvirus infections; however, a major limitation is the requirement for intravenous administration. Two related acyclic nucleoside phosphonates (ANPs), adefovir (PMEA) and tenofovir (PMPA), are active against human immunodeficiency virus or hepatitis B virus but do not have activity against the orthopoxviruses. Therefore, we have evaluated a number of analogs and potential oral prodrugs of these three compounds for their ability to inhibit the replication of vaccinia virus or cowpox virus in tissue culture cells. The most-active compounds within the CDV series were (S)-HPMPA and (butyl l-alaninyl) cyclic HPMPC, with 50% effective concentrations (EC50s) from 4 to 8 μM, compared with 33 to 43 μM for CDV. Although PMEA itself was not active, adefovir dipivoxil {bis[(pivaloyl)oxymethyl] PMEA} and bis(butyl l-alaninyl) PMEA were active against both viruses, and bis(butyl l-alaninyl) PME-N6-(cyclopropyl)DAP and (isopropyl l-alaninyl)phenyl PME-N6-(cyclopropyl)DAP were the most active compounds tested...

‣ Postharvest Variation in Cellulase, Polygalacturonase, and Pectinmethylesterase in Avocado (Persea americana Mill, cv. Fuerte) Fruits in Relation to Respiration and Ethylene Production

Awad, Marcel; Young, Roy E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1979 Português
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Cellulase, polygalacturonase (PG), pectinmethylesterase (PME), respiration, and ethylene production were determined in single “Fuerte” avocado fruits from the day of harvest through the start of fruit breakdown. PME declined from its maximum value at the time of picking to a low level early in the climacteric. PG activity was not detectable in the preclimacteric stage, increased during the climacteric, and continued to increase during the postclimacteric phase to a level three times greater than when the fruit reached the edible soft stage. Cellulase activity was low in the preclimacteric fruit, started to increase just as respiration increased, and reached a level two times greater than at the edible soft stage. Cellulase activity started to increase 3 days before PG activity could be detected. Increased production of ethylene followed the increase in respiration and cellulase activity by about 1.5 days. These results indicate that a close relation exists between the rapid increase in the cell wall-depolymerizing enzymes and the rise in respiration and ethylene production and refocused attention on the role of the cell wall and the associated plasma membrane in the early events of fruit ripening.

‣ VANGUARD1 Encodes a Pectin Methylesterase That Enhances Pollen Tube Growth in the Arabidopsis Style and Transmitting Tract

Jiang, Lixi; Yang, Shu-Lan; Xie, Li-Fen; Puah, Ching San; Zhang, Xue-Qin; Yang, Wei-Cai; Sundaresan, Venkatesan; Ye, De
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /02/2005 Português
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In flowering plants, penetration of the pollen tube through stigma, style, and transmitting tract is essential for delivery of sperm nuclei to the egg cells embedded deeply within female tissues. Despite its importance in plant reproduction, little is known about the underlying molecular mechanisms that regulate the navigation of the pollen tube through the stigma, style, and transmitting tract. Here, we report the identification and characterization of an Arabidopsis thaliana gene, VANGUARD1 (VGD1) that encodes a pectin methylesterase (PME)-homologous protein of 595 amino acids and is required for enhancing the growth of pollen tubes in the style and transmitting tract tissues. VGD1 was expressed specifically in pollen grain and the pollen tube. The VGD1 protein was distributed throughout the pollen grain and pollen tube, including the plasma membrane and cell wall. Functional interruption of VGD1 reduced PME activity in the pollen to 82% of the wild type and greatly retarded the growth of the pollen tube in the style and transmitting tract, resulting in a significant reduction of male fertility. In addition, the vgd1 pollen tubes were unstable and burst more frequently when germinated and grown on in vitro culture medium, compared with wild-type pollen tubes. Our study suggests that the VGD1 product is required for growth of the pollen tube...

‣ Structural Basis for the Interaction between Pectin Methylesterase and a Specific Inhibitor Protein

Di Matteo, Adele; Giovane, Alfonso; Raiola, Alessandro; Camardella, Laura; Bonivento, Daniele; De Lorenzo, Giulia; Cervone, Felice; Bellincampi, Daniela; Tsernoglou, Demetrius
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /03/2005 Português
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Pectin, one of the main components of the plant cell wall, is secreted in a highly methyl-esterified form and subsequently deesterified in muro by pectin methylesterases (PMEs). In many developmental processes, PMEs are regulated by either differential expression or posttranslational control by protein inhibitors (PMEIs). PMEIs are typically active against plant PMEs and ineffective against microbial enzymes. Here, we describe the three-dimensional structure of the complex between the most abundant PME isoform from tomato fruit (Lycopersicon esculentum) and PMEI from kiwi (Actinidia deliciosa) at 1.9-Å resolution. The enzyme folds into a right-handed parallel β-helical structure typical of pectic enzymes. The inhibitor is almost all helical, with four long α-helices aligned in an antiparallel manner in a classical up-and-down four-helical bundle. The two proteins form a stoichiometric 1:1 complex in which the inhibitor covers the shallow cleft of the enzyme where the putative active site is located. The four-helix bundle of the inhibitor packs roughly perpendicular to the main axis of the parallel β-helix of PME, and three helices of the bundle interact with the enzyme. The interaction interface displays a polar character, typical of nonobligate complexes formed by soluble proteins. The structure of the complex gives an insight into the specificity of the inhibitor toward plant PMEs and the mechanism of regulation of these enzymes.

‣ Effect of periodic box size on aqueous molecular dynamics simulation of a DNA dodecamer with particle-mesh Ewald method.

de Souza, O N; Ornstein, R L
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1997 Português
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The particle-mesh Ewald (PME) method is considered to be both efficient and accurate for the evaluation of long-range electrostatic interactions in large macromolecular systems being studied by molecular dynamics simulations. This method assumes "infinite" periodic boundary conditions resembling the symmetry of a crystal environment. Can such a "solid-state" method accurately portray a macromolecular solute such as DNA in solution? To address this issue, we have performed three 1500-ps PME molecular dynamics (MD) simulations, each with a different box size, on the d(CGCGA6CG)-(CGT6CGCG) DNA dodecamer. The smallest box had the DNA solvated by a layer of water molecules of at least 5 A along each orthogonal direction. The intermediate size box and the largest box had the DNA solvated by a layer of water molecules of at least 10 A and 15 A, respectively, along each orthogonal direction. The intermediate size box in the present study is similar to the box size currently chosen by most workers in the field. Based on a comparison of RMSDs and curvature for this single DNA dodecamer sequence, the larger two box sizes do not appear to afford any extra benefit over the smallest box. The implications of this finding are briefly discussed.

‣ Magnetic resonance imaging volumetric and phosphorus 31 magnetic resonance spectroscopy measurements in schizophrenia.

Hinsberger, A D; Williamson, P C; Carr, T J; Stanley, J A; Drost, D J; Densmore, M; MacFabe, G C; Montemurro, D G
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1997 Português
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The purpose of this study was to examine the relationship between phosphorus magnetic resonance spectroscopy (31P MRS) parameters and left prefrontal volumes in both patients with schizophrenia and healthy subjects. 31P MRS parameters and magnetic resonance imaging (MRI) volumetric data were collected in the left prefrontal region in 10 patients with schizophrenia and 10 healthy subjects of comparable age, handedness, sex, educational level, and parental educational level. No correlations were found between any MRS parameter and grey matter volumes in the combined subjects. Phosphomonoester (PME) and grey matter volumes, however, were both correlated negatively with age. PMEs were found to be decreased, and calculated intracellular magnesium ([Mg2+]intra) was found to be increased in the patients with schizophrenia compared with healthy subjects after adjusting for left prefrontal grey and white matter, total brain volume, and age. These findings suggest that cortical grey and white manner volumes are not directly related to PME and [Mg2+]intra abnormalities in schizophrenia patients.

‣ The effects of pregnancy and parturition on phosphorus metabolites in rat uterus studied by 31P nuclear magnetic resonance.

Dawson, M J; Wray, S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1985 Português
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Concentrations of phosphorus metabolites and intracellular pH have been measured in non-pregnant, late-pregnant and post-partum rat uterus using 31P nuclear magnetic resonance (31P n.m.r.). Intact uterine tissue was superfused with oxygenated de-Jalon solution at 4, 20 or 37 degrees C while inside the n.m.r. spectrometer. The phosphocreatine concentration [PCr], was higher and the inorganic phosphate concentration [Pi], lower than values determined by chemical analysis of extracts from both pregnant and non-pregnant rat uterus. [PCr] was 1.4-fold greater in late-pregnant than in non-pregnant rat uterus. Following parturition, large changes were observed in [PCr], [Pi] and in an unidentified metabolite in the phosphomonoester (PME) region of the n.m.r. spectrum. The time course of the recovery of these metabolites to prepregnant values was determined. The [PCr] remained below the non-pregnant value for at least 1 week post-partum and the [Pi] was elevated, compared to the non-pregnant value, during this period. More rapid changes were seen in the [PME], which doubled on day 0 post-partum but almost returned to its non-pregnant value on day 1 post-partum. No significant difference was observed between intracellular pH values in late-pregnant and non-pregnant rat uterus; however...

‣ Changes in brain phosphorus metabolites during the post-natal development of the rat.

Tofts, P; Wray, S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1985 Português
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Changes in brain phosphorus metabolites during the post-natal development of the rat and in neonatal and adult guinea-pigs have been studied in vivo using 31P nuclear magnetic resonance spectroscopy (n.m.r.s.). The brain spectra showed clear differences with age, particularly during the first 3 weeks post-partum. The spectra from 4-day-old rats resembled those of new-born human infants. We suggest that the differences between human and animal brains seen in previously published spectra arise because of an age difference rather than a species difference. The phosphocreatine (PCr) to nucleoside triphosphate (NTP) ratio increased from around 1.0 in 3-day-old rats to 1.8 in adult animals. The adult ratio is larger than that previously reported from in vitro chemical analyses. An unknown compound in the phosphomonoester (PME) region of the spectra predominated in young animals, but decreased in concentration relative to NTP with age and reached adult values by around 2 weeks post-partum. Neonatal guinea-pigs, which are much more developed at birth than the rat, had a significantly greater PCr/NTP ratio than the neonatal rat, but their brain spectra also contained the large PME peak. The intracellular pH of cerebral tissue was estimated to be 7.21 +/- 0.02 and did not show any change with age. The changes we find in the phosphorus compounds in the brain may be of importance in post-natal development...

‣ A novel enzyme activity involving the demethylation of specific partially methylated oligogalacturonides.

Williams, Martin A K; Benen, Jacques A E
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/10/2002 Português
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Studies of the enzymic digestion of pectic substrates using different polygalacturonase (PG) preparations have revealed evidence for a previously unreported enzyme activity carried out by a contaminating enzyme in one of the preparations. This observed activity involves the demethylation of specific oligogalacturonides, namely 2-methyltrigalacturonic acid and 2,3-dimethyltetragalacturonic acid. However, no large-scale demethylation of highly methylated polymeric substrates is found, demonstrating that the enzyme responsible is not a conventional pectin methylesterase (PME). Furthermore, it has been shown that a commercial sample of fungal PME from Aspergillus niger demethylates all of the oligogalacturonides present as primary products of endo-PG digestion, in contrast with the activity observed here. On the basis of the known methyl ester distribution of the endo-PG-generated fragments and knowledge of which of these oligogalacturonides are demethylated, it is concluded that the observed activity can be explained by the existence of an exo-acting methylesterase that attacks the non-reducing end of the oligogalacturonide molecules.

‣ Partially esterified oligogalacturonides are the preferred substrates for pectin methylesterase of Aspergillus niger.

van Alebeek, Gert-Jan W M; van Scherpenzeel, Katrien; Beldman, Gerrit; Schols, Henk A; Voragen, Alphons G J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/05/2003 Português
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Investigations on the mode of action of Aspergillus niger pectin methylesterase (PME) towards differently C(6)- and C(1)-substituted oligogalacturonides (oligoGal p A) are described. De-esterification of methyl-esterified (un)saturated oligoGal p A proceeds via a specific pattern, depending on the degree of polymerization. Initially, a first methyl ester of the oligomer is hydrolysed, resulting in one free carboxyl group. Subsequently, this first product is preferred as a substrate and is de-esterified for a second time. This product is then accumulated and hereafter de-esterified further to the final product, i.e. oligoGal p A containing one methyl ester located at the non-reducing end residue for both saturated and unsaturated oligoGal p A, as found by post-source decay matrix-assisted laser-desorption/ionization-time-of-flight MS. The saturated hexamer is an exception to this: three methyl esters are removed very rapidly, instead of two methyl esters. When unsaturated oligoGal p A were used, the formation of the end product differed slightly, suggesting that the unsaturated bond at the non-reducing end influences the de-esterification process. In vivo, PME prefers methyl esters, but the enzyme appeared to be tolerant for other C(6)- and C(1)-substituents. Changing the type of ester (ethyl esterification) or addition of a methyl glycoside (C(1)) only reduced the activity or had no effect respectively. The specific product pattern was identical for all methyl- and ethyl-esterified oligoGal p A and methyl-glycosidated oligoGal p A...

‣ An inactive protein phosphatase 2A population is associated with methylesterase and can be re-activated by the phosphotyrosyl phosphatase activator.

Longin, Sari; Jordens, Jan; Martens, Ellen; Stevens, Ilse; Janssens, Veerle; Rondelez, Evelien; De Baere, Ivo; Derua, Rita; Waelkens, Etienne; Goris, Jozef; Van Hoof, Christine
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/05/2004 Português
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We have described recently the purification and cloning of PP2A (protein phosphatase 2A) leucine carboxylmethyltransferase. We studied the purification of a PP2A-specific methylesterase that co-purifies with PP2A and found that it is tightly associated with an inactive dimeric or trimeric form of PP2A. These inactive enzyme forms could be reactivated as Ser/Thr phosphatase by PTPA (phosphotyrosyl phosphatase activator of PP2A). PTPA was described previously by our group as a protein that stimulates the in vitro phosphotyrosyl phosphatase activity of PP2A; however, PP2A-specific methyltransferase could not bring about the activation. The PTPA activation could be distinguished from the Mn2+ stimulation observed with some inactive forms of PP2A, also found associated with PME-1 (phosphatase methylesterase 1). We discuss a potential new function for PME-1 as an enzyme that stabilizes an inactivated pool of PP2A.

‣ Importance of explicit salt ions for protein stability in molecular dynamics simulation.

Ibragimova, G T; Wade, R C
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1998 Português
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The accurate and efficient treatment of electrostatic interactions is one of the challenging problems of molecular dynamics simulation. Truncation procedures such as switching or shifting energies or forces lead to artifacts and significantly reduced accuracy. The particle mesh Ewald (PME) method is one approach to overcome these problems by providing a computationally efficient means of calculating all long-range electrostatic interactions in a periodic simulation box by use of fast Fourier transformation techniques. For the application of the PME method to the simulation of a protein with a net charge in aqueous solution, counterions are added to neutralize the system. The usual procedure is to add charge-balancing counterions close to charged residues to neutralize the protein surface. In the present article, we show that for MD simulation of a small protein of marginal stability, the YAP-WW domain, explicit modeling of 0.2 M ionic strength (in addition to the charge-balancing counterions) is necessary to maintain a stable protein structure. Without explicit ions throughout the periodic simulation box, the charge-balancing counterions on the protein surface diffuse away from the protein, resulting in destruction of the beta-sheet secondary structure of the WW domain.

‣ Molecular basis of the activity of the phytopathogen pectin methylesterase

Fries, Markus; Ihrig, Jessica; Brocklehurst, Keith; Shevchik, Vladimir E; Pickersgill, Richard W
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Português
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We provide a mechanism for the activity of pectin methylesterase (PME), the enzyme that catalyses the essential first step in bacterial invasion of plant tissues. The complexes formed in the crystal using specifically methylated pectins, together with kinetic measurements of directed mutants, provide clear insights at atomic resolution into the specificity and the processive action of the Erwinia chrysanthemi enzyme. Product complexes provide additional snapshots along the reaction coordinate. We previously revealed that PME is a novel aspartic-esterase possessing parallel β-helix architecture and now show that the two conserved aspartates are the nucleophile and general acid-base in the mechanism, respectively. Other conserved residues at the catalytic centre are shown to be essential for substrate binding or transition state stabilisation. The preferential binding of methylated sugar residues upstream of the catalytic site, and demethylated residues downstream, drives the enzyme along the pectin molecule and accounts for the sequential pattern of demethylation produced by both bacterial and plant PMEs.

‣ SIK1 is part of a cell sodium-sensing network that regulates active sodium transport through a calcium-dependent process

Sjöström, Mattias; Stenström, Karin; Eneling, Kristina; Zwiller, Jean; Katz, Adrian I.; Takemori, Hiroshi; Bertorello, Alejandro M.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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In mammalian cells, active sodium transport and its derived functions (e.g., plasma membrane potential) are dictated by the activity of the Na+,K+-ATPase (NK), whose regulation is essential for maintaining cell volume and composition, as well as other vital cell functions. Here we report the existence of a salt-inducible kinase-1 (SIK1) that associates constitutively with the NK regulatory complex and is responsible for increases in its catalytic activity following small elevations in intracellular sodium concentrations. Increases in intracellular sodium are paralleled by elevations in intracellular calcium through the reversible Na+/Ca2+ exchanger, leading to the activation of SIK1 (Thr-322 phosphorylation) by a calcium calmodulin-dependent kinase. Activation of SIK1 results in the dephosphorylation of the NK α-subunit and an increase in its catalytic activity. A protein phosphatase 2A/phosphatase methylesterase-1 (PME-1) complex, which constitutively associates with the NK α-subunit, is activated by SIK1 through phosphorylation of PME-1 and its dissociation from the complex. These observations illustrate the existence of a distinct intracellular signaling network, with SIK1 at its core, which is triggered by a monovalent cation (Na+) and links sodium permeability to its active transport.

‣ Dynamical Motions of Lipids and a Finite Size Effect in Simulations of Bilayers

Klauda, Jeffery B.; Brooks, Bernard R.; Pastor, Richard W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 14/10/2006 Português
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Molecular dynamics (MD) simulations of dipalmitoylphosphatidylcholine (DPPC) bilayers composed of 72 and 288 lipids are used to examine system size dependence on dynamical properties associated with the particle-mesh Ewald (PME) treatment of electrostatic interactions. The lateral diffusion constant, Dℓ, is 2.92×10−7 and 0.95×10−7 cm2/s for 72 and 288 lipids, respectively. This dramatic finite size effect originates from the correlation length of lipid diffusion, which extends to next-nearest neighbors in the 288 lipid system. Consequently, diffusional events in smaller systems can propagate across the boundaries of the periodic box. The internal dynamics of lipids calculated from the PME simulations are independent of the system size. Specifically, reorientational correlation functions for the slowly relaxing phosphorous-glycerol hydrogen, phosphorous-nitrogen vectors, and more rapidly relaxing CH vectors in the aliphatic chains are equivalent for the 72 and 288 lipid simulations. A third MD simulation of a bilayer with 72 lipids using spherical force-shift electrostatic cutoffs resulted in interdigitated chains, thereby rendering this cutoff method inappropriate.

‣ Effects of Economic Shocks on Children’s Employment and Schooling in Brazil

Duryea, Suzanne; Lam, David; Levison, Deborah
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/2007 Português
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This paper uses longitudinal employment survey data to analyze the impact of household economic shocks on the schooling and employment transitions of young people in metropolitan Brazil. The paper uses data on over 100,000 children ages 10–16 from Brazil’s Monthly Employment Survey (PME) from 1982 to 1999. Taking advantage of the rotating panels in the PME, we compare households in which the male household head becomes unemployed during a four-month period with households in which the head is continuously employed. Probit regressions indicate that an unemployment shock significantly increases the probability that a child enters the labor force, drops out of school, and fails to advance in school. The effects can be large, implying increases of as much as 50% in the probability of entering employment for 16-year-old girls. In contrast, shocks occurring after the school year do not have significant effects, suggesting that these results are not due to unobserved characteristics of households that experience unemployment shocks. The results suggest that some households are not able to absorb short-run economic shocks, with negative consequences for children.