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Activation Mechanism (activation + mechanism)
Selected AbstractsActivation Mechanism and Infiltration Kinetic for Pressureless Melt Infiltration of Ti Activated Al2O3 Preforms by High Melting Alloy,ADVANCED ENGINEERING MATERIALS, Issue 8 2009Srdan Vasi The infiltration mechanism of X3CrNi13-4 in titanium activated porous alumina preforms has been studied. Investigations revealed isolated steel-covered titanium particles beyond the infiltration front. The only transport path possible for the steel to form such wetted islands is through the gas phase. Supersaturation due to the mixing of the steel gas phase with the titanium rich gas phase over the activator particle surfaces is proposed as condensation mechanism. Progressive condensation leads to the formation of a melt network, which serves as pathway for the original steel melt to infiltrate the preforms and to fill the remaining pore space in the non-wetting X3CrNi13-4/Ti-Al2O3 sytem. [source] Retina expresses a novel variant of the ryanodine receptorEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2007Varda Shoshan-Barmatz Abstract Calcium released from intracellular stores via the ryanodine receptor (RyR) mediates a variety of signalling processes. We previously showed that retina expresses the three known types of RyR, but retinal membrane preparations exhibit unique characteristics such as Ca2+ -independent [3H]ryanodine-binding and inhibition by caffeine. We have heretofore suggested that the major retinal RyR isoform is novel. The present study aimed to identify this receptor isoform and to localize RyR in mammalian retina. Immunoblotting with specific and pan-antibodies showed that the major retinal RyR has a mobility similar to that of RyR2 or RyR3. Real-time PCR revealed that the major type is RyR2, and RT-PCR followed by sequencing showed a transcript that encodes a protein with ~ 99% identity to RyR2, yet lacking two regions of seven and 12 amino acids and including an additional insertion of eight amino acids. An antibody against RyR2 localized this type to somas and primary dendrites of most retinal neurons. An antibody against RyR1 localized RyR to most somas but also revealed staining in photoreceptor outer segments, concentrated on the disk membranes at their rim. The ryanodine-binding properties and the electrophoretic mobility of RyR from the outer segments were similar to those of the whole retinal preparation. The results thus identify a novel variant of RyR2 which can contribute to regulating photoreceptor Ca2+ concentrations. The restricted localization of the outer segment RyR to the disk rim suggests that its activation mechanism involves a coupling between retinal RyR and the cGMP-gated channel. [source] Kinetics of intra- and intermolecular zymogen activation with formation of an enzyme,zymogen complexFEBS JOURNAL, Issue 1 2005Matilde Esther Fuentes A mathematical description was made of an autocatalytic zymogen activation mechanism involving both intra- and intermolecular routes. The reversible formation of an active intermediary enzyme,zymogen complex was included in the intermolecular activation route, thus allowing a Michaelis,Menten constant to be defined for the activation of the zymogen towards the active enzyme. Time,concentration equations describing the evolution of the species involved in the system were obtained. In addition, we have derived the corresponding kinetic equations for particular cases of the general model studied. Experimental design and kinetic data analysis procedures to evaluate the kinetic parameters, based on the derived kinetic equations, are suggested. The validity of the results obtained were checked by using simulated progress curves of the species involved. The model is generally good enough to be applied to the experimental kinetic study of the activation of different zymogens of physiological interest. The system is illustrated by following the transformation kinetics of pepsinogen into pepsin. [source] Synthesis of Fluorenes via the Palladium-Catalyzed 5- exo-dig Annulation of o -AlkynylbiarylsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009Natalia Chernyak Abstract The direct palladium-catalyzed intramolecular hydroarylation of o -alkynylbiaryls proceeded in a highly stereoselective manner producing fluorenes 2, the products of 5- exo-dig cyclization, in excellent yields. The cascade intermolecular arylation, incorporated in this transformation, allowed for the efficient synthesis of fully substituted fluorenes 12. These cyclizations proceed more rapidly with electron-deficient benzene rings which, in combination with a substantial isotope effect observed, strongly supports a CH activation mechanism for the key annulation step. [source] Substrate activation of butyrylcholinesterase and substrate inhibition of acetylcholinesterase by 3,3-dimethylbutyl- N - n -butylcarbamate and 2-trimethylsilyl-ethyl- N - n -butylcarbamateJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 1 2007Shyh-Ying Chiou Abstract Carbamates are used to treat Alzheimer's disease. These compounds inhibit acetylcholinesterase and butyrylcholinesterase. The goal of this work is to use the substrate analogs of butyrylcholinesterase, 3,3-dimethylbutyl- N - n -butylcarbamate (1) and 2-trimethylsilyl-ethyl- N - n -butylcarbamate (2) to probe the substrate activation mechanism of butyrylcholinesterase. Compounds 1 and 2 are characterized as the pseudo substrate inhibitors of acetylcholinesterase; however, compounds 1 and 2 are characterized as the essential activators of butyrylcholinesterase. Therefore, compounds 1 and 2 mimic the substrate in the acetylcholinesterase-catalyzed reactions, but the behavior of compounds 1 and 2 mimics the substrate activation in the butyrylcholinesterase-catalyzed reactions. © 2007 Wiley Periodicals, Inc. J Biochem Mol Toxicol 21:24,31, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20158 [source] Differential Effects of Ethanol on Signal TransductionALCOHOLISM, Issue 1 2000Gail H. Levine Background: PC12 pheochromocytoma cells were used as a model to study the effect of long-term ethanol exposure on signal transduction systems. In PC12 cells, the agonist bradykinin stimulates a phospholipase C specific for inositol-containing phospholipids and a phospholipase D specific for phosphatidylcholine. Methods: PC12 cells were grown in monolayer and cultured in the presence and absence of 1% ethanol for 5 days. After this period, bradykinin-stimulated phospholipase C and D were measured. The effect of long-term ethanol on the bradykinin-mediated activation of mitogen-activated protein (MAP) kinase was also measured. Results: In cells exposed to 1% ethanol for 5 days, bradykinin-stimulated phospholipase D was greatly attenuated, whereas bradykinin-stimulated phospholipase C was not altered. The tyrosine kinase inhibitor, genistein, blocked the bradykinin-mediated activation of phospholipase D but did not affect the stimulation of phospholipase C. However, long-term ethanol treatment did not attenuate the ability of bradykinin to activate MAP kinase, which suggests that ethanol did not have a general effect on all tyrosine kinase pathways. Conclusions: Ethanol has a differential effect on signal transduction in PC12 cells. Activation of phospholipase D may be mediated by a kinase, whereas the activation of phospholipase C is probably mediated by the guanine nucleotide binding protein, Gq. Because of these differences in activation mechanism, the pathways may adapt differently to long-term exposure to ethanol. [source] Rapid autocatalytic activation of the M4 metalloprotease aureolysin is controlled by a conserved N-terminal fungalysin-thermolysin-propeptide domainMOLECULAR MICROBIOLOGY, Issue 6 2008Nicholas N. Nickerson Summary The Staphylococcus aureus proteolytic cascade consists of a metalloprotease aureolysin (Aur), which activates a serine protease zymogen proSspA, which in turn activates the SspB cysteine protease. As with other M4 metalloproteases, including elastase of Pseudomonas aeruginosa, the propeptide of proAur contains an N-terminal fungalysin-thermolysin-propeptide (FTP) domain. Autocatalytic activation of proAur was initiated by processing at T85,L86 in the FTP domain. This differed from the mechanism described for proElastase, where the FTP domain has an RY motif in place of TL86, and processing occurred at the junction of the propeptide and metalloprotease domains, which remained as an inactive complex during passage across the outer membrane. When TL86 in the FTP domain was replaced with RY, an intact N-terminal propeptide was secreted, but the M4 metalloprotease domain was degraded. Consequently, this segment of the FTP domain promotes intramolecular processing of proAur while bestowing a chaperone function, but discourages processing within the FTP domain of proElastase, where activation must be co-ordinated with passage across a second membrane. We conclude that the FTP domain of proAur is adapted to facilitate a rapid autocatalytic activation mechanism, consistent with the role or proAur as initiator of the staphylococcal proteolytic cascade. [source] Structural mechanisms of multidrug recognition and regulation by bacterial multidrug transcription factorsMOLECULAR MICROBIOLOGY, Issue 4 2002Maria A. Schumacher Summary The increase in bacterial resistance to multiple drugs represents a serious and growing health risk. One component of multidrug resistance (MDR) is a group of multidrug transporters that are often regulated at the transcriptional level by repressors and/or activators. Some of these transcription factors are also multidrug-binding proteins, frequently recognizing the same array of drugs that are effluxed by the transporters that they regulate. How a single protein can recognize such chemically disparate compounds is an intriguing question from a structural standpoint and an important question in future drug development endeavours. Unlike the multidrug transporters, the cytosolic multidrug-binding regulatory proteins are more tractable systems for structural analyses. Here, we describe recent crystallographic studies on MarR, BmrR and QacR, three bacterial transcription regulators that are also multidrug-binding proteins. Although our understanding of multidrug binding and transcriptional regulation by MarR is in its initial stages, the structure of a BmrR,TPP+,DNA complex has revealed important insights into the novel transcription activation mechanism of the MerR family, and the structures of a QacR,DNA complex and QacR bound to six different drugs have revealed not only the mechanism of induction of this repressor but has afforded the first view of any MDR protein bound to multiple drugs. [source] Coupling of Protonation Switches During Rhodopsin Activation,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2007Reiner Vogel Recent studies of the activation mechanism of rhodopsin involving Fourier-transform infrared spectroscopy and a combination of chromophore modifications and site-directed mutagenesis reveal an allosteric coupling between two protonation switches. In particular, the ring and the 9-methyl group of the all- trans retinal chromophore serve to couple two proton-dependent activation steps: proton uptake by a cytoplasmic network between transmembrane (TM) helices 3 and 6 around the conserved ERY (Glu-Arg-Tyr) motif and disruption of a salt bridge between the retinal protonated Schiff base (PSB) and a protein counterion in the TM core of the receptor. Retinal analogs lacking the ring or 9-methyl group are only partial agonists,the conformational equilibrium between inactive Meta I and active Meta II photoproduct states is shifted to Meta I. An artificial pigment was engineered, in which the ring of retinal was removed and the PSB salt bridge was weakened by fluorination of C14 of the retinal polyene. These modifications abolished allosteric coupling of the proton switches and resulted in a stabilized Meta I state with a deprotonated Schiff base (Meta ISB). This state had a partial Meta II-like conformation due to disruption of the PSB salt bridge, but still lacked the cytoplasmic proton uptake reaction characteristic of the final transition to Meta II. As activation of native rhodopsin is known to involve deprotonation of the retinal Schiff base prior to formation of Meta II, this Meta ISB state may serve as a model for the structural characterization of a key transient species in the activation pathway of a prototypical G protein-coupled receptor. [source] A combined structural dynamics approach identifies a putative switch in factor VIIa employed by tissue factor to initiate blood coagulationPROTEIN SCIENCE, Issue 4 2007Ole H. Olsen Abstract Coagulation factor VIIa (FVIIa) requires tissue factor (TF) to attain full catalytic competency and to initiate blood coagulation. In this study, the mechanism by which TF allosterically activates FVIIa is investigated by a structural dynamics approach that combines molecular dynamics (MD) simulations and hydrogen/deuterium exchange (HX) mass spectrometry on free and TF-bound FVIIa. The differences in conformational dynamics from MD simulations are shown to be confined to regions of FVIIa observed to undergo structural stabilization as judged by HX experiments, especially implicating activation loop 3 (residues 365,374{216,225}) of the so-called activation domain and the 170-loop (residues 313,322{170A,175}) succeeding the TF-binding helix. The latter finding is corroborated by experiments demonstrating rapid deglycosylation of Asn322 in free FVIIa by PNGase F but almost complete protection in the presence of TF or an active-site inhibitor. Based on MD simulations, a key switch of the TF-induced structural changes is identified as the interacting pair Leu305{163} and Phe374{225} in FVIIa, whose mutual conformations are guided by the presence of TF and observed to be closely linked to the structural stability of activation loop 3. Altogether, our findings strongly support an allosteric activation mechanism initiated by the stabilization of the Leu305{163}/Phe374{225} pair, which, in turn, stabilizes activation loop 3 and the S1 and S3 substrate pockets, the activation pocket, and N-terminal insertion. [source] Mechano-biology of skeletal muscle hypertrophy and regeneration: Possible mechanism of stretch-induced activation of resident myogenic stem cellsANIMAL SCIENCE JOURNAL, Issue 1 2010Ryuichi TATSUMI ABSTRACT In undamaged postnatal muscle fibers with normal contraction and relaxation activities, quiescent satellite cells of resident myogenic stem cells are interposed between the overlying external lamina and the sarcolemma of a subjacent mature muscle fiber. When muscle is injured, exercised, overused or mechanically stretched, these cells are activated to enter the cell proliferation cycle, divide, differentiate, and fuse with the adjacent muscle fiber, and are responsible for regeneration and work-induced hypertrophy of muscle fibers. Therefore, a mechanism must exist to translate mechanical changes in muscle tissue into chemical signals that can activate satellite cells. Recent studies of satellite cells or single muscle fibers in culture and in vivo demonstrated the essential role of hepatocyte growth factor (HGF) and nitric oxide (NO) radical in the activation pathway. These experiments have also reported that mechanically stretching satellite cells or living skeletal muscles triggers the activation by rapid release of HGF from its extracellular tethering and the subsequent presentation to the receptor c-met. HGF release has been shown to rely on calcium-calmodulin formation and NO radical production in satellite cells and/or muscle fibers in response to the mechanical perturbation, and depend on the subsequent up-regulation of matrix metalloproteinase (MMP) activity. These results indicate that the activation mechanism is a cascade of events including calcium ion influx, calcium-calmodulin formation, NO synthase activation, NO radical production, MMP activation, HGF release and binding to c-met. Better understanding of ,mechano-biology' on the satellite cell activation is essential for designing procedures that could enhance muscle growth and repair activities in meat-animal agriculture and also in neuromuscular disease and aging in humans. [source] Development of molecular immunoassay system for probiotics via toll-like receptors based on food immunologyANIMAL SCIENCE JOURNAL, Issue 1 2008Haruki KITAZAWA ABSTRACT Recent interest has focused on the importance of intestinal immunity for the host defense, but to date, not much is known about the underlying mechanisms. The toll-like receptor (TLR) family plays an important role in host defense through recognizing bacterial pathogen-associated molecular patterns. Our recent research on the physiological function of food products has investigated the immunoregulatory effects of probiotic lactic acid bacteria (LAB) via TLR. Studies of swine, which often substitute for a human model, have demonstrated intestinal immunoregulation by the probiotic LAB mediated by TLR in the gut. On the basis of our study, efforts have also been made to develop a molecular immunoassay system for probiotic LAB and find novel immunostimulatory DNA sequences from probiotics and high potential immunobiotic LAB strains via TLR signaling. These findings may provide important clues at the molecular level on TLR signal transduction pathways and recognition mechanisms for the ligands. They also provide impetus to further delineate the activation mechanism of the innate immune response. In addition to identifying immunoregulatory factor immunogenics from LAB, a better understanding of intestinal immune regulation through cytokine networks holds out promise for basic food immunology research and the development of immunobiotic foods to prevent specific diseases. [source] X-ray structure of the metcyano form of dehaloperoxidase from Amphitrite ornata: evidence for photoreductive dissociation of the iron,cyanide bondACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2010V. S. De Serrano X-ray crystal structures of the metcyano form of dehaloperoxidase-hemoglobin (DHP A) from Amphitrite ornata (DHPCN) and the C73S mutant of DHP A (C73SCN) were determined using synchrotron radiation in order to further investigate the geometry of diatomic ligands coordinated to the heme iron. The DHPCN structure was also determined using a rotating-anode source. The structures show evidence of photoreduction of the iron accompanied by dissociation of bound cyanide ion (CN,) that depend on the intensity of the X-ray radiation and the exposure time. The electron density is consistent with diatomic molecules located in two sites in the distal pocket of DHPCN. However, the identities of the diatomic ligands at these two sites are not uniquely determined by the electron-density map. Consequently, density functional theory calculations were conducted in order to determine whether the bond lengths, angles and dissociation energies are consistent with bound CN, or O2 in the iron-bound site. In addition, molecular-dynamics simulations were carried out in order to determine whether the dynamics are consistent with trapped CN, or O2 in the second site of the distal pocket. Based on these calculations and comparison with a previously determined X-ray crystal structure of the C73S,O2 form of DHP [de Serrano et al. (2007), Acta Cryst. D63, 1094,1101], it is concluded that CN, is gradually replaced by O2 as crystalline DHP is photoreduced at 100,K. The ease of photoreduction of DHP A is consistent with the reduction potential, but suggests an alternative activation mechanism for DHP A compared with other peroxidases, which typically have reduction potentials that are 0.5,V more negative. The lability of CN, at 100,K suggests that the distal pocket of DHP A has greater flexibility than most other hemoglobins. [source] Muscarinic cationic current in gastrointestinal smooth muscles: signal transduction and role in contractionAUTONOMIC & AUTACOID PHARMACOLOGY, Issue 3 2006T. Unno Summary 1 The muscarinic receptor plays a key role in the parasympathetic nervous control of various peripheral tissues including gastrointestinal tract. The neurotransmitter acetylcholine, via activating muscarinic receptors that exist in smooth muscle, produces its contraction. 2 There is the opening of cationic channels as an underlying mechanism. The opening of cationic channels results in influxes of Ca2+ via the channels into the cell and also via voltage-dependent Ca2+ channels which secondarily opened in response to the depolarization, providing an amount of Ca2+ for activation of the contractile proteins. 3 Electrophysiological and pharmacological studies have shown that the cationic channels as well as muscarinic receptors exist in many visceral smooth muscle cells. However, the activation mechanisms of the cationic channels are still unclear. 4 In this article, we summarize the current knowledge of the muscarinic receptor-operated cationic channels, focusing on the receptor subtype, G protein and other signalling molecules that are involved in activation of these channels and on the molecular characterisitics of the channel. This will improve strategies aimed at developing new selective pharmacological agents and understanding the activation mechanism and functions of these channels in physiological systems. [source] Characterization of G proteins involved in activation of nonselective cation channels by endothelinB receptorBRITISH JOURNAL OF PHARMACOLOGY, Issue 7 2002Yoshifumi Kawanabe We recently demonstrated that endothelin-1 (ET-1) activates two types of Ca2+ -permeable nonselective cation channels (NSCC-1 and NSCC-2) in Chinese hamster ovary cells expressing endothelinB receptors (CHO-ETBR) that couple with Gq and Gi. The purpose of the present study was to identify the G proteins involved in the activation of these Ca2+ channels by ET-1. For this purpose, we constructed CHO cells expressing an unpalmitoylated (Cys402Cys403 Cys405,Ser402Ser403Ser405) ETBR (CHO-SerETBR) and ETBR truncated at the cytoplasmic tail downstream of Cys403 (CHO-ETBR,403). Based on the data obtained from actin stress fibre formation, CHO-ETBR couple with G13. Therefore, CHO-ETBR couple with Gq, Gi and G13. CHO-SerETBR and CHO-ETBR,403 couple with G13 and Gq, respectively. ET-1 activated NSCC-1 in CHO-ETBR preincubated with phospholipase C (PLC) inhibitor, U73122, and in CHO-SerETBR. On the other hand, ET-1 failed to activate Ca2+ channels in CHO-ETBR,403. Microinjection of dominant negative mutants of G13 (G13G225A) abolished activation of NSCC-1 and NSCC-2 in CHO-ETBR and that of NSCC-1 in CHO-SerETBR. Y-27632, a specific Rho-associated kinase (ROCK) inhibitor, did not affect the ET-1-induced transient and sustained increase in [Ca2+]i in CHO-ETBR. These results indicate that (1) the cytoplasmic tail downstream of the palmitoylation sites of ETBR, but not the palmitoylation site itself, is essential for coupling with G13, (2) the activation mechanism of each Ca2+ channel by ET-1 is different in CHO-ETBR. NSCC-1 activation depends on G13 -dependent cascade, and NSCC-2 activation depends on both Gq/PLC- and G13 -dependent cascades. Moreover, ROCK-dependent cascade is not involved in the activation of these channels. British Journal of Pharmacology (2002) 136, 1015,1022. doi:10.1038/sj.bjp.0704805 [source] Toll-like receptor signalling on Tregs: to suppress or not to suppress?IMMUNOLOGY, Issue 4 2008Wendy W. C. Van Maren Summary To balance self-tolerance and immunity against pathogens or tumours, the immune system depends on both activation mechanisms and down-regulatory mechanisms. Immunologists have long been focusing on activation mechanisms, and a major breakthrough was the identification of the Toll-like receptor (TLR) family of proteins. TLRs recognize conserved molecular patterns present on pathogens, including bacteria, viruses, fungi and protozoa. Pathogen recognition via TLRs activates the innate as well as the adaptive immune response. The discovery of a suppressive T-cell subset that constitutively expresses the interleukin (IL)-2 receptor ,-chain (CD25) has boosted efforts to investigate the negative regulation of immune responses. It is now well appreciated that these regulatory T cells (Tregs) play a pivotal role in controlling immune function. Interestingly, recent studies revealed that TLR2 signalling affects Treg expansion and function. This review will focus on the presence and influence of different TLRs on T lymphocytes, including Tregs, and their role in cancer. [source] Cross-talk between the insulin-like growth factor (IGF) axis and membrane integrins to regulate cell physiologyJOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2010James Beattie The biology of cross-talk between activated growth factor receptors and cell-surface integrins is an area which has attracted much interest in recent years (Schwartz and Ginsberg, 2002). This review discusses the relationship between the insulin-like growth factor (IGF) axis and cell-surface integrin receptors in the regulation of various aspects of cell physiology. Key to these interactions are signals transmitted between integrins and the IGF-I receptor (IGF-IR) when either or both are bound to their cognate ligands and we will review the current state of knowledge in this area. The IGF axis comprises many molecular components and we will also discuss the potential role of these species in cross-talk with the integrin receptor. With respect to integrin ligands, we will mainly focus on the well-characterized interactions of the two extracellular matrix (ECM) glycoproteins fibronectin (FN) and vitronectin (VN) with cell-surface ligands, and, how this affects activity through the IGF axis. However, we will also highlight the importance of other integrin activation mechanisms and their impact on IGF activity. J. Cell. Physiol. 224: 605,611, 2010. © 2010 Wiley-Liss, Inc. [source] Platelet integrin ,IIb,3: activation mechanismsJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 7 2007Y.-Q. MA Summary., Integrin ,IIb,3 plays a critical role in platelet aggregation, a central response in hemostasis and thrombosis. This function of ,IIb,3 depends upon a transition from a resting to an activated state such that it acquires the capacity to bind soluble ligands. Diverse platelet agonists alter the cytoplasmic domain of ,IIb,3 and initiate a conformational change that traverses the transmembrane region and ultimately triggers rearrangements in the extracellular domain to permit ligand binding. The membrane-proximal regions of ,IIb and ,3 cytoplasmic tails, together with the transmembrane segments of the subunits, contact each other to form a complex which restrains the integrin in the resting state. It is unclasping of this complex that induces integrin activation. This clasping/unclasping process is influenced by multiple cytoplasmic tail binding partners. Among them, talin appears to be a critical trigger of ,IIb,3 activation, but other binding partners, which function as activators or suppressors, are likely to act as co-regulators of integrin activation. [source] The Alternative Oxidase: in vivo Regulation and FunctionPLANT BIOLOGY, Issue 1 2003F. F. Millenaar Abstract: This review focuses on the biochemical regulation and function of the alternative oxidase in vivo. About 10 years ago, two activation mechanisms were discovered in isolated mitochondria, namely activation by reducing sulfur bonds in the protein and activation by an allosteric effect of pyruvate. It was proposed that plants would have a regulatory mechanism to modify alternative oxidase activity in vivo. However, more recent studies have shown that these two activation mechanisms may not play such an important role in regulation of alternative oxidase activity in vivo after all. Pyruvate and reduction of the sulfide bonds in the protein are definitely required for alternative oxidase activity, but they do not appear to be regulating the activity in vivo. Despite the energy wasting nature of the alternative oxidase, there was no obvious physiological function for the pathway for many years. It is now more clear that the alternative oxidase can prevent the production of excess reactive oxygen species radicals by stabilizing the redox state of the mitochondrial ubiquinone pool, while allowing continued activity of the citric acid cycle. This may be important under conditions when the NADH supply is relatively high (reductant overflow), or when the cytochrome pathway is restrained. The cytochrome pathway might be inhibited by naturally occurring cyanide, nitric oxide, sulfide, high concentrations of CO2, low temperatures, or by limited phosphate supply. [source] Effects of in vitro exposure to ozone and/or hyperoxia on superoxide dismutase, catalase, glutathione and lipid peroxidation in red blood cells and plasma of rainbow trout, Oncorhynchus mykiss (Walbaum)AQUACULTURE RESEARCH, Issue 3 2002O Ritola Abstract In aquaculture, ozone is used as a disinfectant. In its production, extensive amounts of oxygen are formed resulting in hyperoxic conditions in culture units. Both ozone and hyperoxia have the potential to be toxic via pro-oxidant mechanisms and to activate antioxidant defence systems in cultured species. To eliminate systemic effects, blood of rainbow trout, Oncorhynchus mykiss (Walbaum), was exposed in vitro for 5 min to ozone/hyperoxia or hyperoxia, and changes in antioxidant defences and lipid peroxidation were measured after exposure. Ozone exposure caused severe damage in red blood cells (rbc) detected as increased lipid peroxidation and oxidized glutathione (GSSG) levels in both plasma and rbc. Oxygen exposure alone increased intracellular lipid peroxidation and GSSG levels 10 min after exposure and was not evident in the plasma at any time. Ozone, but not oxygen exposure, decreased reduced glutathione (GSH) levels in plasma, and the changes were negatively correlated with increased lipid peroxidation in rbc, indicating that extracellular GSH has a dynamic role in the protection of rbc from direct oxidation by ozone. Both ozone and hyperoxic conditions increased superoxide dismutase (SOD) activity in rbc 3 and 6 h after exposure. In contrast, catalase activity was only increased 10 min after oxygen exposure, suggesting other catalase activation mechanisms rather than enzyme induction. The recovery of lipid peroxidation and GSSG levels in rbc after hyperoxia, but not ozone exposure, indicated a capacity to defend against hyperoxia-produced oxidative damage, but an overwhelming of antioxidant defences by ozone in rainbow trout rbc in vitro. [source] High-resolution diffracting crystals of intrinsically active p38, MAP kinase: a case study for low-throughput approachesACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2007Ron Diskin p38 MAP kinases are central signalling molecules that mediate cellular responses to numerous environmental conditions and signalling molecules. Their proper function is required for many processes, including stress response, apoptosis, differentiation, growth and even learning and memory. Abnormal activity of p38 MAP kinases is associated with the aetiology of many diseases, making understanding their activation mechanisms highly critical. In this respect, mechanistic insights may be derived from structural studies of recently developed intrinsically active p38, mutants. Unlike wild-type p38,, which routinely crystallized, the active mutants caused severe difficulties during the crystallization process. The main hindrance was found to be protein heterogeneity, which was meticulously resolved by genetically modifying the recombinant protein and optimizing the expression and purification protocols. The success in obtaining crystallizable proteins strongly emphasizes that in certain cases, high-throughput techniques (crystallization robots) together with low-throughput approaches, with careful monitoring and analysis of the results, are essential. [source] Muscarinic cationic current in gastrointestinal smooth muscles: signal transduction and role in contractionAUTONOMIC & AUTACOID PHARMACOLOGY, Issue 3 2006T. Unno Summary 1 The muscarinic receptor plays a key role in the parasympathetic nervous control of various peripheral tissues including gastrointestinal tract. The neurotransmitter acetylcholine, via activating muscarinic receptors that exist in smooth muscle, produces its contraction. 2 There is the opening of cationic channels as an underlying mechanism. The opening of cationic channels results in influxes of Ca2+ via the channels into the cell and also via voltage-dependent Ca2+ channels which secondarily opened in response to the depolarization, providing an amount of Ca2+ for activation of the contractile proteins. 3 Electrophysiological and pharmacological studies have shown that the cationic channels as well as muscarinic receptors exist in many visceral smooth muscle cells. However, the activation mechanisms of the cationic channels are still unclear. 4 In this article, we summarize the current knowledge of the muscarinic receptor-operated cationic channels, focusing on the receptor subtype, G protein and other signalling molecules that are involved in activation of these channels and on the molecular characterisitics of the channel. This will improve strategies aimed at developing new selective pharmacological agents and understanding the activation mechanism and functions of these channels in physiological systems. [source] Mammalian NDR/LATS protein kinases in hippo tumor suppressor signalingBIOFACTORS, Issue 4 2009Alexander Hergovich Abstract The NDR/LATS family of kinases is a subgroup of the AGC group of protein kinases and is conserved from lower eukaryotes to humans. Like other AGC kinases, NDR/LATS kinases require phosphorylation of conserved Ser/Thr residues for activation. On the one hand, binding of the coactivator MOB to NDR/LATS allows autophosphorylation. On the other hand, MST kinases directly phosphorylate NDR/LATS kinases. In addition to our understanding of the molecular activation mechanisms, recent studies have shown that LATS kinases play a central role in Hippo/SWH (Salvador/Warts/Hippo) tumor suppressor pathways, which coordinate cell proliferation and apoptosis by regulating proto-oncogenes, such as YAP and TAZ. In this review, we summarize current knowledge of Merlin/MST/SAV/MOB/LATS/NDR/YAP/TAZ networks (also termed mammalian Hippo signaling) and their roles in mammalian cellular transformation. © 2009 International Union of Biochemistry and Molecular Biology, Inc. [source] Pharmacology of transient receptor potential melastatin channels in the vasculatureBRITISH JOURNAL OF PHARMACOLOGY, Issue 8 2010Alexander Zholos Mammalian transient receptor potential melastatin (TRPM) non-selective cation channels, the largest TRP subfamily, are widely expressed in excitable and non-excitable cells where they perform diverse functions ranging from detection of cold, taste, osmolarity, redox state and pH to control of Mg2+ homeostasis and cell proliferation or death. Recently, TRPM gene expression has been identified in vascular smooth muscles with dominance of the TRPM8 channel. There has been in parallel considerable progress in decoding the functional roles of several TRPMs in the vasculature. This research on native cells is aided by the knowledge of the activation mechanisms and pharmacological properties of heterologously expressed TRPM subtypes. This paper summarizes the present state of knowledge of vascular TRPM channels and outlines several anticipated directions of future research in this area. [source] Design of a complement mannose-binding lectin pathway-specific activation system applicable at low serum dilutionsCLINICAL & EXPERIMENTAL IMMUNOLOGY, Issue 3 2006M. Harboe Summary Recently we showed that alternative pathway (AP) amplification was responsible for more than 80% of specific classical pathway-induced terminal pathway activation under physiological conditions. The present study aimed to design a system for specific lectin pathway (LP) activation applicable at low serum dilutions with a fully functional AP. Comparison between activation of normal human serum (NHS), a mannose-binding lectin (MBL) homozygous D/D -deficient serum, and sera deficient in C1q and C2, all diluted 1 : 2, was essential to document optimal conditions for LP specificity. Mannan on the solid phase of enzyme-linked immunosorbent assay (ELISA) plates was used for activation, showing 0·5 µg mannan/well to give optimal conditions because at this concentration a good signal was preserved for C4 and TCC deposition in NHS, whereas the C3 deposition observed in C2-deficient serum at higher mannan concentrations reached nadir at 0·5 µg/well, indicating a lack of direct AP activation under these conditions. Pooled NHS and C1q-deficient serum gave the same degree of C4 and terminal complement complex (TCC) deposition, whereas deposition of these products was not obtained with MBL-deficient serum. Reconstitution with purified MBL, however, restored the depositions. A blocking anti-MBL monoclonal antibody (mAb) completely abolished the complement deposition, in contrast to a non-inhibiting anti-MBL mAb. Activation of C2-deficient serum induced C4 deposition similar to NHS, but negligible deposition of C3 and TCC, confirming the lack of direct activation of AP. Thus, this assay is unique in being LP-specific at low serum dilution and thus particularly suitable to study LP activation mechanisms and the role of AP amplification under physiological conditions. [source] Multiple Mechanisms of Thrombosis Complicating Atherosclerotic PlaquesCLINICAL CARDIOLOGY, Issue S6 2000Peter Libby M.D. Abstract Atherosclerosis is a highly prevalent disorder and remains a leading cause of morbidity and mortality in the United States. Recent advances in vascular biology have led to a better understanding of the mechanisms underlying atherogenesis. The central role played by plaque disruption, and by adhesion, activation, and aggregation of platelets that trigger activation of the coagulation cascade in the pathogenesis of acute thrombotic events is also better understood. Combination antithrombotic therapy targeting various platelet activation mechanisms and the coagulation cascade may help optimize the management of atherosclerosis. [source] Rational Analyses of Information Foraging on the WebCOGNITIVE SCIENCE - A MULTIDISCIPLINARY JOURNAL, Issue 3 2005Peter Pirolli Abstract This article describes rational analyses and cognitive models of Web users developed within information foraging theory. This is done by following the rational analysis methodology of (a) characterizing the problems posed by the environment, (b) developing rational analyses of behavioral solutions to those problems, and (c) developing cognitive models that approach the realization of those solutions. Navigation choice is modeled as a random utility model that uses spreading activation mechanisms that link proximal cues (information scent) that occur in Web browsers to internal user goals. Web-site leaving is modeled as an ongoing assessment by the Web user of the expected benefits of continuing at a Web site as opposed to going elsewhere. These cost,benefit assessments are also based on spreading activation models of information scent. Evaluations include a computational model of Web user behavior called Scent-Based Navigation and Information Foraging in the ACT Architecture, and the Law of Surfing, which characterizes the empirical distribution of the length of paths of visitors at a Web site. [source] | |||||||||||||||||||||||||||||||