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Second Mechanism (second + mechanism)
Selected AbstractsLow level of cuticular hydrocarbons in a parasitoid of a solitary digger wasp and its potential for concealmentENTOMOLOGICAL SCIENCE, Issue 1 2009Johannes KROISS Abstract Insect cuticular hydrocarbons (CHC) play a role as semiochemicals in many host,parasite systems and chemical mimicry or camouflage is a well-known mechanism of parasites to evade detection by the host. The cuckoo wasp Hedychrum rutilans (Hymenoptera, Chrysididae) is a parasitoid of larvae of the European beewolf Philanthus triangulum (Hymenoptera, Crabronidae). Females chemically mimic the cuticular hydrocarbons of their hosts to avoid detection and countermeasures when entering the host nest for oviposition. Here we report on a possible second mechanism of the chrysidid wasp H. rutilans to evade detection: the amount of CHC/mm2 of cuticle is only approximately one-fifth compared to its beewolf host. Furthermore, we show that surprisingly large amounts of CHC of beewolf females can be found on the walls of the underground nest. Potentially, these hydrocarbons might constitute a background odor against which the cuckoo wasps or their chemical traces have to be perceived by the beewolf. The reduction in the amount of CHC of the cuckoo wasps might be equivalent to a dilution of recognition cues, especially against the background odor of the nest walls, and might provide a means to escape detection within the nest due to "chemical insignificance". [source] The Role of Amine,B(C6F5)3 Adducts in the Catalytic Reduction of Imines with H2: A Computational StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2009Timofei Privalov Abstract This study thoroughly examines the potential energy surfaces (PESs) of two possible mechanisms for reduction of imines by B(C6F5)3 and H2. The key reaction steps of the first catalytic mechanism, which is the focus of our study, are: (i) the uptake of H2 by a thermally activated amine,B(C6F5)3 species; (ii) proton transfer from the NH2+ moiety of [RNH2CH2R,]+[HB(C6F5)3], to the imine; (iii) nucleophillic attack of the C-center of the iminium ion by the BH, group. The potential energy barriers of the latter, as determined by calculating the evolution of the H-bonded complex of an imine and [RNH2CH2R,]+[HB(C6F5)3], in toluene, are around 10 kcal,mol,1 each. In the second mechanism, only imines serve as basic partners of B(C6F5)3 in the H2 activation, which affords an [RN(H)CHR,]+[HB(C6F5)3], ion pair; direct reduction then proceeds via nucleophilic attack of the C-center by the BH, in [RN(H)CHR,]+[HB(C6F5)3],. This route becomes catalytic when the product amine is released into the solvent and B(C6F5)3 is re-used for H2 activation. Upon taking into account the association energy of an amine,B(C6F5)3 adduct [,9.5 kcal,mol,1 for tBuN(H)CH2Ph and B(C6F5)3 in toluene], the potential energy barrier for H2 uptake by an imine and B(C6F5)3 increases to 14.5 kcal,mol,1. We report a somewhat lower potential energy barrier for H2 uptake by thermally activated amine,B(C6F5)3 adducts [12.7 kcal,mol,1 for the B-N adduct of tBuN(H)CH2Ph and B(C6F5)3 in toluene], although the difference between the two H2 activationbarriers is within the expected error of the computational method. Two catalytic routes are compared based on B3LYP-computed PESs in solvent (toluene).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Seasonal trophic dynamics affect zooplankton community variabilityFRESHWATER BIOLOGY, Issue 11 2009BEATRIX E. BEISNER Summary 1. The degree to which communities are variable may be affected by the ecological conditions to which they are exposed and can affect their propensity to form alternative states. We examined the influence of two common ecological factors, predation and seasonal successional stage, on the variability in community composition of herbivorous pond plankton. In a highly replicated, two factor, mesocosm experiment we determined whether beta diversity was affected by seasonal successional stage of the community (two levels), by fish predation (presence/absence) or by their interaction. 2. Several significant changes were found in the composition of the rotifer, cladoceran and copepod assemblages. Most cladoceran abundances showed sharp declines in the presence of fish, while some rotifers, as well as their assemblage species richness, responded favourably to fish. The copepod assemblage was composed of omnivorous and carnivorous species, which added invertebrate predation to the experiment and which intensified as the season progressed. Copepods showed responses to fish predation that depended on seasonal successional stage of the initial community, because of changes in their stage structure and edibility as they grew from nauplii to adults. 3. Community variability was consistently high at the end of each month-long experimental period for both cladoceran and rotifer assemblages, except under two conditions. In the early season treatments, the rotifer assemblages were more consistent (lower beta diversity) in the presence of fish. This was attributed to high population growth rates for rotifers under these ecological conditions because of reduced copepod predation on them through a trophic cascade from fish. Low community variability was also observed in the late season for rotifers when fish were excluded and, as a result, they were exposed to high invertebrate predation from cyclopoid copepods. 4. Results from the early season support theoretical predictions that when community size increases, variability in composition should decline because of an increase in competitive processes over stochastic ones. Late season results suggest that a second mechanism, specialist predation, can also reduce prey community variability. Our study demonstrates that plankton communities may be more predictable under certain trophic web configurations and challenges ecologists to find ways to incorporate such inherent variability into experiments and community theory. [source] Changes in chromatin structure and methylation of the human interleukin-1, gene during monopoiesisIMMUNOLOGY, Issue 3 2010Inga Wessels Summary Interleukin-1, (IL-1,) induces the expression of a variety of proteins responsible for acute inflammation and chronic inflammatory diseases. However, the molecular regulation of IL-1, expression in myeloid differentiation has not been elucidated. In this study the chromatin structure of the IL-1, promoter and the impact of methylation on IL-1, expression in monocytic development were examined. The results revealed that the IL-1, promoter was inaccessible in undifferentiated promyeloid HL-60 cells but highly accessible in differentiated monocytic cells which additionally acquired the ability to produce IL-1,. Accessibilities of differentiated cells were comparable to those of primary monocytes. Lipopolysaccharide (LPS) stimulation did not affect promoter accessibility in promyeloid and monocytic HL-60 cells, demonstrating that the chromatin remodelling of the IL-1, promoter depends on differentiation and not on the transcriptional status of the cell. Demethylation via 5-aza-2,-deoxycytodine led to the induction of IL-1, expression in undifferentiated and differentiated cells, which could be increased after LPS stimulation. Our data indicate that the IL-1, promoter is reorganized into an open poised conformation during monopoiesis being a privilege of mature monocytes but not of the entire myeloid lineage. As a second mechanism, IL-1, expression is regulated by methylation acting independently of the developmental stage of myeloid cells. [source] Escape in space from enemies: a comparison between stands with and without enhanced densities of the spruce bark beetleAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2007Leif Martin Schroeder Abstract 1,Populations of the spruce bark beetle, Ips typographus (L.), are known to grow rapidly in storm-disturbed stands as a result of relaxation from intraspecific competition. In the present study, it was tested whether a second mechanism, escape in space from natural enemies, also contributes to the rapid population increase. 2,The experiment was conducted during the initiation phase of five local outbreaks of I. typographus triggered by a storm-disturbance in November 1995 in southern Sweden. 3,The impact of natural enemies on the ratio of increase (number of daughters per mother) of I. typographus was compared pairwise between disturbed stands with high numbers of storm-felled trees and undisturbed stands without wind-felled trees. 4,Enemy impact was assessed by comparing the ratio of increase in uncaged (exposed to enemies) and caged (protected from enemies) bolts colonized by I. typographus prior to being placed in the stands. The experiment was conducted in the second and third summers after the storm-felling. 5,Enemy impact was about twice as high in stands without wind-felled trees compared with in stands with wind-felled trees in the second summer whereas there was no significant difference between the stand types in the third summer. 6,The result demonstrates that spatial escape from enemies contributes to the rapid population growth of I. typographus after storm-disturbances. [source] Two Mechanisms of Synaptic Vesicle Recycling in Rat Brain Nerve TerminalsJOURNAL OF NEUROCHEMISTRY, Issue 4 2000Michael A. Cousin Abstract: KCl and 4-aminopyridine (4-AP) evoke glutamate release from rat brain cortical nerve terminals by voltage clamping or by Na+ channel-generated repetitive action potentials, respectively. Stimulation by 4-AP but not KCl is largely mediated by protein kinase C (PKC). To determine whether KCl and 4-AP utilise the same mechanism to release glutamate, we correlated glutamate release with release of the hydrophobic synaptic vesicle (SV) marker FM2-10. A strong correlation was observed for increasing concentrations of KCl and after application of phorbol 12-myristate 13-acetate (PMA) or staurosporine. The parallel increase in exocytosis measured by two approaches suggested it occurred by a PKC-independent mechanism involving complete fusion of SVs with the plasma membrane. At low concentrations of 4-AP, alone or with staurosporine, glutamate and FM2-10 release also correlated. However, higher concentrations of 4-AP or of 4-AP plus PMA greatly increased glutamate release but did not further increase FM2-10 release. This divergence suggests that 4-AP recruits an additional mechanism of release during strong stimulation that is PKC dependent and is superimposed upon the first mechanism. This second mechanism is characteristic of kiss-and-run, which is not detectable by styryl dyes. Our data suggest that glutamate release in nerve terminals occurs via two mechanisms: (1) complete SV fusion, which is PKC independent; and (2) a kiss-and-run-like mechanism, which is PKC dependent. Recruitment of a second release mechanism may be a widespread means to facilitate neurotransmitter release in central neurons. [source] Isoniazid-resistance conferring mutations in Mycobacterium tuberculosis KatG: Catalase, peroxidase, and INH-NADH adduct formation activitiesPROTEIN SCIENCE, Issue 3 2010Christine E. Cade Abstract Mycobacterium tuberculosis catalase-peroxidase (KatG) is a bifunctional hemoprotein that has been shown to activate isoniazid (INH), a pro-drug that is integral to frontline antituberculosis treatments. The activated species, presumed to be an isonicotinoyl radical, couples to NAD+/NADH forming an isoniazid-NADH adduct that ultimately confers anti-tubercular activity. To better understand the mechanisms of isoniazid activation as well as the origins of KatG-derived INH-resistance, we have compared the catalytic properties (including the ability to form the INH-NADH adduct) of the wild-type enzyme to 23 KatG mutants which have been associated with isoniazid resistance in clinical M. tuberculosis isolates. Neither catalase nor peroxidase activities, the two inherent enzymatic functions of KatG, were found to correlate with isoniazid resistance. Furthermore, catalase function was lost in mutants which lacked the Met-Tyr-Trp crosslink, the biogenic cofactor in KatG which has been previously shown to be integral to this activity. The presence or absence of the crosslink itself, however, was also found to not correlate with INH resistance. The KatG resistance-conferring mutants were then assayed for their ability to generate the INH-NADH adduct in the presence of peroxide (t -BuOOH and H2O2), superoxide, and no exogenous oxidant (air-only background control). The results demonstrate that residue location plays a critical role in determining INH-resistance mechanisms associated with INH activation; however, different mutations at the same location can produce vastly different reactivities that are oxidant-specific. Furthermore, the data can be interpreted to suggest the presence of a second mechanism of INH-resistance that is not correlated with the formation of the INH-NADH adduct. [source] Collision-induced dissociation of glycero phospholipids using electrospray ion-trap mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2001Åsmund Larsen Characterisation of phospholipids was achieved using collision-induced dissociation (CID) with an ion-trap mass spectrometer. The product ions were compared with those obtained with a triple quadrupole mass spectrometer. In the negative ion mode the product ions were mainly sn -1 and sn -2 lyso-phospholipids with neutral loss of ketene in combination with neutral loss of the polar head group. Less abundant product ions were sn -1 and sn -2 carboxylate anions. CID using a triple quadrupole mass spectrometer, however, gave primarily the sn -1 and sn -2 carboxylate anions together with lyso-phosphatidic acid with neutral loss of water. For the ion trap a charge-remote-type mechanism is proposed for formation of the lyso-phospholipid product ions by loss of ,-hydrogen on the fatty acid moiety, electron rearrangement and neutral loss of ketene. A second mechanism involves nucleophilic attack of the phosphate oxygen on the sn -1 and sn -2 glycerol backbone to form carboxylate anions with neutral loss of cyclo lyso-phospholipids. CID (MS3 and MS4) of the lyso-phospholipids using the ion-trap gave the same carboxylate anions as those obtained with a triple quadrupole instrument where multiple collisions in the collision cell are expected to occur. The data demonstrate that phospholipid species determination can be performed by using LC/MSn with an ion-trap mass spectrometer with detection of the lyso-phospholipid anions. The ion-trap showed no loss in sensitivity in full scan MSn compared to multiple reaction monitoring data acquisition. In combination with on-line liquid chromatography this feature makes the ion-trap useful in the scanning modes for rapid screening of low concentrations of phospholipid species in biological samples as recently described (Uran S, Larsen,Å, Jacobsen PB, Skotland T. J. Chromatogr. B 2001; 758: 265). Copyright © 2001 John Wiley & Sons, Ltd. [source] NS0 cell damage by high gas velocity sparging in protein-free and cholesterol-free culturesBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2008Ying Zhu Abstract Recent developments in high cell density and high productivity fed-batch animal cell cultures have placed a high demand on oxygenation and carbon dioxide removal in bioreactors. The high oxygen demand is often met by increasing agitation and sparging rates of air/O2 in the bioreactors. However, as we demonstrate in this study, an increase of gas sparging can result in cell damage at the sparger site due to high gas entrance velocities. Previous studies have showed that gas bubble breakup at the culture surface was primarily responsible for cell damage in sparged bioreactors. Such cell damage can be reduced by use of surfactants such as Pluronic F-68 in the culture. In our results, where NS0 cells were grown in a protein-free and cholesterol-free medium containing 0.5 g/L Pluronic F-68, high gas entrance velocity at the sparger site was observed as the second mechanism for cell damage. Experiments were performed in scaled-down spinners to model the effect of hydrodynamic force resulting from high gas velocities on antibody-producing NS0 cells. Cell growth and cell death were described by first-order kinetics. Cell death rate constant increased significantly from 0.04 to 0.18 day,1 with increasing gas entrance velocity from 2.3 to 82.9 m/s at the sparger site. The critical gas entrance velocity for the NS0 cell line studied was found to be ,30 m/s; velocities greater than 30 m/s caused cell damage which resulted in reduced viability and consequently reduced antibody production. Observations from a second cholesterol-independent NS0 cell line confirmed the occurrence of cell damage due to high gas velocities. Increasing the concentration of Pluronic F-68 from 0.5 to 2 g/L had no additional protective effect on cell damage associated with high gas velocity at the sparger. The results of gas velocity analysis for cell damage have been applied in two case studies of large-scale antibody manufacturing. The first is a troubleshooting study for antibody production carried out in a 600 L bioreactor, and the second is the development of a gas sparger design for a large bioreactor scale (e.g., 10,000 L) for antibody manufacturing. Biotechnol. Bioeng. 2008;101: 751,760. © 2008 Wiley Periodicals, Inc. [source] | |||||||||||||