Antineoplasic Drug Methotrexate Redox Mechanism Using a Glassy Carbon Electrode

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Seed survival and dispersal of an endemic Atlantic forest palm: the combined effects of defaunation and forest fragmentation

About 45 palm species occur in the Atlantic forest of Brazil, and most of them are affected by loss of seed dispersers resulting from forest fragmentation and hunting. Here we report the effects of habitat loss and defaunation on the seed dispersal system of an endemic palm, Astrocaryum aculeatissimum. We evaluated seed removal, insect and rodent seed predation, and scatter-hoarding in nine sites, ranging from 19 ha to 79 000 ha. We report the seedling, juvenile and adult palm densities in this range of sites. Endocarps remaining beneath the parent palm had a higher probability of being preyed upon by insects in small, mostly fragmented and more defaunated sites. The frequency of successful seed removal, scatter-hoarding and consumption by rodents increased in the larger, less defaunated sites. Successful removal and dispersal collapsed in small (< 1000 ha), highly defaunated sites and frequently resulted in low densities of both seedlings and juveniles. Our results indicate that a large fraction of Atlantic forest palms that rely on scatter-hoarding rodents may become regionally extinct due to forest fragmentation and defaunation. Current management practices including palm extraction and hunting pressure have a lasting effect on Atlantic forest palm regeneration by severely limiting successful recruitment of prereproductive individuals.(c) 2006 the Linnean Society of London.

New catalytic mechanism for human purine nucleoside phosphorylase

Human purine nucleoside phosphorylase has been submitted to intensive structure-based design of inhibitors, most of them using low-resolution structures of human PNP. Recently, several structures of human PNP have been reported, which allowed redefinition of the active site and understanding of the structural basis for inhibition of PNP by acyclovir and immucillin-H. Based on previously solved human PNP structures, we proposed here a new catalytic mechanism for human PNP, which is supported by crystallographic studies and explains previously determined kinetic data. (C) 2004 Elsevier B.V. All rights reserved.

The kinetic mechanism of human uridine phosphorylase 1: Towards the development of enzyme inhibitors for cancer chemotherapy

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

The chromosomes and the sex determining mechanism of Scaphura nigra (Orthoptera, Ensifera, Tettigoniidae, Phaneropterinae).

Scaphum nigra has a uniquechromosomecomplement among approximately 100 species studied so far belonging to the subfamily Phaneropterinae. It is formed by 2n ([male]) = 26 and a FN = 29 and derived from the ancestral karyotype of the group 2n ([male]) = 31, FN = 31, by means of two centric fusions and one tandem fusion. The first between the X chromosome and a medium-sized autosome giving rise to a neo-XY sex chromosome mechanism of recent origin, and the second between two acrocentric ones, the bigger and a medium size, that gave rise to a large submetacentric element whose length is very uncommon in the subfamily. This process has created a bimodal karyotype that contrasts with the majority in this group, whose chromosomes usually can be arranged in a decreasing order of size. A third rearrangement incorporating the chromatin of a medium-sized autosome to the bigger one, explains the reduction observed in the number of chromosomes and the enlarged size of the submetacentric elements. These features demonstrate the effectiveness of chromosome number, their morphology and the change of the sex mechanism as useful tools for taxonomy.

Brown Recluse Spider Venom: Proteomic Analysis and Proposal of a Putative Mechanism of Action

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

Profiling the Proteome of the Venom from the Social Wasp Polybia paulista: A Clue to Understand the Envenoming Mechanism

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

Effects of forest fragmentation, anthropogenic edges and fruit colour on the consumption of ornithocoric fruits

We investigated effects of fruit colour (red, black or white), habitat (anthropogenic edges and forest interior) and fragment size on the removal of artificial fruits in semideciduous forests in south-east Brazil. Eight forest fragments ranging from 251 to 36,000 ha were used. We used artificial fruits, which were placed on shrubs between I and 2 m in height and checked after 48 and 96 h for peck marks in the fruits. All three variables affected the probability of consumption of our fruit models. Red and black fruits were statistically more pecked than the white fruits. The probability of fruit consumption was lower in the interior than at the edge and less in small than in large fragments. However, the decrease fruit consumption in small compared with large fragments was more accentuated for red and black fruits than for white fruits. Our results show that habitat reduction and edges affect the chances of a fruit being eaten by birds, which may ultimately affect plant fitness in forest fragments. (C) 2003 Elsevier B.V. Ltd. All rights reserved.

Development of the insulin secretion mechanism in fetal and neonatal rat pancreatic B-cells: response to glucose, K+, theophylline, and carbamylcholine

We studied the development of the insulin secretion mechanism in the pancreas of fetal (19- and 21-day-old), neonatal (3-day-old), and adult (90-day-old) rats in response to stimulation with 8.3 or 16.7 mM glucose, 30 mM K+, 5 mM theophylline (Theo) and 200 µM carbamylcholine (Cch). No effect of glucose or high K+ was observed on the pancreas from 19-day-old fetuses, whereas Theo and Cch significantly increased insulin secretion at this age (82 and 127% above basal levels, respectively). High K+ also failed to alter the insulin secretion in the pancreas from 21-day-old fetuses, whereas 8.3 mM and 16.7 mM glucose significantly stimulated insulin release by 41 and 54% above basal levels, respectively. Similar results were obtained with Theo and Cch. A more marked effect of glucose on insulin secretion was observed in the pancreas of 3-day-old rats, reaching 84 and 179% above basal levels with 8.3 mM and 16.7 mM glucose, respectively. At this age, both Theo and Cch increased insulin secretion to close to two-times basal levels. In islets from adult rats, 8.3 mM and 16.7 mM glucose, Theo, and Cch increased the insulin release by 104, 193, 318 and 396% above basal levels, respectively. These data indicate that pancreatic B-cells from 19-day-old fetuses were already sensitive to stimuli that use either cAMP or IP3 and DAG as second messengers, but insensitive to stimuli such as glucose and high K+ that induce membrane depolarization. The greater effect of glucose on insulin secretion during the neonatal period indicates that this period is crucial for the maturation of the glucose-sensing mechanism in B-cells.

An explanatory mechanism for the different decline in limb strength in older women

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Annexin 1 peptides protect against experimental myocardial ischemia-reperfusion: analysis of their mechanism of action

Myocardial reperfusion injury is associated with the infiltration of blood-borne polymorphonuclear leukocytes. We have previous described the protection afforded by annexin 1 (ANXA1) in an experimental model of rat myocardial ischemia-reperfusion (IR) injury. We examined the 1) amino acid region of ANXA1 that retained the protective effect in a model of rat heart IR; 2) changes in endogenous ANXA1 in relation to the IR induced damage and after pharmacological modulation; and 3) potential involvement of the formyl peptide receptor (FPR) in the protective action displayed by ANXA1 peptides. Administration of peptide Ac2-26 at 0, 30, and 60 min postreperfusion produced a significant protection against IR injury, and this was associated with reduced myeloperoxidase activity and IL-1 beta levels in the infarcted heart. Western blotting and electron microscopy analyses showed that IR heart had increased ANXA1 expression in the injured tissue, associated mainly with the infiltrated leukocytes. Finally, an antagonist to the FPR receptor selectively inhibited the protective action of peptide ANXA1 and its derived peptides against IR injury. Altogether, these data provide further insight into the protective effect of ANXA1 and its mimetics and a rationale for a clinical use for drugs developed from this line of research.

Structural insights into the catalytic mechanism of sphingomyelinases D and evolutionary relationship to glycerophosphodiester phosphodiesterases

Spider venom sphingomyelinases D catalyze the hydrolysis of sphingomyelin via an Mg2+ ion-dependent acid-base catalytic mechanism which involves two histidines. In the crystal structure of the sulfate free enzyme determined at 1.85 angstrom resolution, the metal ion is tetrahedrally coordinated instead of the trigonal-bipyramidal coordination observed in the sulfate bound form. The observed hyperpolarized state of His47 requires a revision of the previously suggested catalytic mechanism. Molecular modeling indicates that the fundamental structural features important for catalysis are fully conserved in both classes of SMases D and that the Class II SMases D contain an additional intra-chain disulphide bridge (Cys53-Cys201). Structural analysis suggests that the highly homologous enzyme from Loxosceles bonetti is unable to hydrolyze sphingomyelin due to the 95G1y -> Asn and 134Pro -> Glu mutations that modify the local charge and hydrophobicity of the interfacial face. Structural and sequence comparisons confirm the evolutionary relationship between sphingomyelinases D and the glicerophosphodiester phosphoesterases which utilize a similar catalytic mechanism. (c) 2006 Elsevier B.V. All rights reserved.

Structural basis for metal ion coordination and the catalytic mechanism of sphingomyelinases D

Sphingomyelinases D (SMases D) from Loxosceles spider venom are the principal toxins responsible for the manifestation of dermonecrosis, intravascular hemolysis, and acute renal failure, which can result in death. These enzymes catalyze the hydrolysis of sphingomyelin, resulting in the formation of ceramide 1-phosphate and choline or the hydrolysis of lysophosphatidyl choline, generating the lipid mediator lysophosphatidic acid. This report represents the first crystal structure of a member of the sphingomyelinase D family from Loxosceles laeta (SMase I), which has been determined at 1.75-angstrom resolution using the quick cryo-soaking technique and phases obtained from a single iodine derivative and data collected from a conventional rotating anode x-ray source. SMase I folds as an (alpha/beta)(8) barrel, the interfacial and catalytic sites encompass hydrophobic loops and a negatively charged surface. Substrate binding and/or the transition state are stabilized by a Mg2+ ion, which is coordinated by Glu(32), Asp(34), Asp(91), and solvent molecules. In the proposed acid base catalytic mechanism, His(12) and His(47) play key roles and are supported by a network of hydrogen bonds between Asp(34), Asp(52), Trp(230), Asp(233), and Asn(252).

Enzymatic toxins from snake venom: structural characterization and mechanism of catalysis

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

Transient and d.c. analysis of the operation mechanism of light-emitting electrochemical cells

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