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991.
992.
Hydrolysis of several N alpha-substituted L-arginine 4-nitroanilides with porcine pancreatic kallikrein was studied under different conditions of pH, temperature, and salt concentration. At high substrate concentrations a deviation from Michaelis-Menten kinetics was observed with a significant increase in the hydrolysis rates of almost all substrates. Kinetic data were analyzed on the assumption that porcine pancreatic kallikrein presents an additional binding site with lower affinity for the substrate. Binding to this auxiliary site gives rise to a modulated enzyme species which can hydrolyze an additional molecule of the substrate through a second catalytic pathway. The values of both Michaelis-Menten and catalytic rate constants were higher for the modulated species than for the free enzyme, suggesting a mechanism of enzyme activation by substrate. Kinetic data indicated similar substrate requirements for binding at the primary and auxiliary sites of the enzyme. Tris(hydroxymethyl)aminomethane hydrochloride and NaCl were shown to alter the kinetic parameters of the hydrolysis of N alpha-acetyl-L-Phe-L-Arg 4-nitroanilide by porcine pancreatic kallikrein but not the enzyme activation pattern (ratio of the catalytic constants for the activated and the free enzyme forms). Similar observations were made when the hydrolysis of D-Val-L-Leu-L-Arg 4-nitroanilide was studied under different pH and temperature conditions. 相似文献
993.
Silviya R. Stateva Valentina Salas Gustavo Benaim Margarita Menéndez Dolores Solís Antonio Villalobo 《PloS one》2015,10(4)
Calmodulin (CaM) phosphorylated at different serine/threonine and tyrosine residues is known to exert differential regulatory effects on a variety of CaM-binding enzymes as compared to non-phosphorylated CaM. In this report we describe the preparation and characterization of a series of phospho-(Y)-mimetic CaM mutants in which either one or the two tyrosine residues present in CaM (Y99 and Y138) were substituted to aspartic acid or glutamic acid. It was expected that the negative charge of the respective carboxyl group of these amino acids mimics the negative charge of phosphate and reproduce the effects that distinct phospho-(Y)-CaM species may have on target proteins. We describe some physicochemical properties of these CaM mutants as compared to wild type CaM, after their expression in Escherichia coli and purification to homogeneity, including: i) changes in their electrophoretic mobility in the absence and presence of Ca2+; ii) ultraviolet (UV) light absorption spectra, far- and near-UV circular dichroism data; iii) thermal stability in the absence and presence of Ca2+; and iv) Tb3+-emitted fluorescence upon tyrosine excitation. We also describe some biochemical properties of these CaM mutants, such as their differential phosphorylation by the tyrosine kinase c-Src, and their action as compared to wild type CaM, on the activity of two CaM-dependent enzymes: cyclic nucleotide phosphodiesterase 1 (PDE1) and endothelial nitric oxide synthase (eNOS) assayed in vitro. 相似文献
994.
Andrea Franzetti Isabella Gandolfi Valentina Bertolini Chiara Raimondi Marco Piscitello Maddalena Papacchini Giuseppina Bestetti 《International biodeterioration & biodegradation》2011,65(7):1095-1099
Bacteria able to produce biological emulsifiers were isolated from different environments using different isolation media with the aim of discovering the widest diversity. The phylogenetic diversity of the isolates was evaluated by 16S rRNA gene analysis. Among 190 isolated strains, 127 released extracellular emulsifiers able to stabilize oil-water emulsions when grown on low-cost substrates. Among these, the 35 isolates that showed the highest emulsifier production on different substrates were found to belong to 16 different bacterial genera. Overall, this is the first systematic study of the diversity of bioemulsifier-producing bacteria and of their ability to produce bioemulsifiers on low-cost substrates. 相似文献
995.
M. J. Prado M. V. Gonzalez S. Romo M. T. Herrera 《Plant Cell, Tissue and Organ Culture》2007,88(1):1-10
The present work reports on a study of plant regeneration carried out with callus from the leaf blades and petioles of field-grown
male adult kiwifruit plants (Actinidia deliciosa (Chev.) Liang and Ferguson). The cultivars used were ‘Tomuri’ and clone A, a selected male plant grown in north western Spain.
The best shoot induction conditions were obtained in ‘Tomuri’ leaf blades cultured in K(h) medium in the presence of 23 μM
Zeatin and 0.1 μM NAA. Under these conditions, more than 80% of organogenic callus induction was observed, with an average
of 14 new shoots in the second subculture. The initial length of the shoots affected shoot elongation, which was accomplished
by culturing isolated shoots in K(h) medium with half-strength salts, supplemented with 0.4 μM Zeatin and 0.1 μM NAA. A possible
detrimental long-term effect of cytokinins on shoot elongation can account for the results, since elongation was not observed
until 1 month of culture in elongation medium. For rooting, shoots (1 cm in length) were basally immersed in a 5 mM IBA solution
for 15 s, and transferred to half-strength K(h) basal medium. Regenerated plants were acclimated in a sterile peat:perlite
substrate for 10 days, and then transferred to soil. AFLP analysis was accomplished with 15 primer combinations from which
13 showed reproducible and well-resolved bands, producing a total of 1321 fragments from which 1281 were polymorphic (97%).
A dendrogram was constructed using both monomorphic and polymorphic bands, showing genetic variation among field-grown plants
and tissue culture-derived regenerants. 相似文献
996.
Marco Brunoldi Giorgio Bozzini Alessandra Casale Pietro Corvisiero Daniele Grosso Nicodemo Magnoli Jessica Alessi Carlo Nike Bianchi Alberta Mandich Carla Morri Paolo Povero Maurizio Wurtz Christian Melchiorre Gianni Viano Valentina Cappanera Giorgio Fanciulli Massimiliano Bei Nicola Stasi Mauro Taiuti 《PloS one》2016,11(1)
Within the framework of the EU Life+ project named LIFE09 NAT/IT/000190 ARION, a permanent automated real-time passive acoustic monitoring system for the improvement of the conservation status of the transient and resident population of bottlenose dolphin (Tursiops truncatus) has been implemented and installed in the Portofino Marine Protected Area (MPA), Ligurian Sea. The system is able to detect the simultaneous presence of dolphins and boats in the area and to give their position in real time. This information is used to prevent collisions by diffusing warning messages to all the categories involved (tourists, professional fishermen and so on). The system consists of two gps-synchronized acoustic units, based on a particular type of marine buoy (elastic beacon), deployed about 1 km off the Portofino headland. Each one is equipped with a four-hydrophone array and an onboard acquisition system which can record the typical social communication whistles emitted by the dolphins and the sound emitted by boat engines. Signals are pre-filtered, digitized and then broadcast to the ground station via wi-fi. The raw data are elaborated to get the direction of the acoustic target to each unit, and hence the position of dolphins and boats in real time by triangulation. 相似文献
997.
Mariana Claudia Allievi María Mercedes Palomino Mariano Prado Acosta Leonardo Lanati Sandra Mónica Ruzal Carmen Sánchez-Rivas 《PloS one》2014,9(10)
Lysinibacillus sphaericus strains belonging the antigenic group H5a5b produce spores with larvicidal activity against larvae of Culex mosquitoes. C7, a new isolated strain, which presents similar biochemical characteristics and Bin toxins in their spores as the reference strain 2362, was, however, more active against larvae of Culex mosquitoes. The contribution of the surface layer protein (S-layer) to this behaviour was envisaged since this envelope protein has been implicated in the pathogenicity of several bacilli, and we had previously reported its association to spores. Microscopic observation by immunofluorescence detection with anti S-layer antibody in the spores confirms their attachment. S-layers and BinA and BinB toxins formed high molecular weight multimers in spores as shown by SDS-PAGE and western blot detection. Purified S-layer from both L. sphaericus C7 and 2362 strain cultures was by itself toxic against Culex sp larvae, however, that from C7 strain was also toxic against Aedes aegypti. Synergistic effect between purified S-layer and spore-crystal preparations was observed against Culex sp. and Aedes aegypti larvae. This effect was more evident with the C7 strain. In silico analyses of the S-layer sequence suggest the presence of chitin-binding and hemolytic domains. Both biochemical characteristics were detected for both S-layers strains that must justify their contribution to pathogenicity. 相似文献
998.
Cyclophilin D Modulates Mitochondrial F0F1-ATP Synthase by Interacting with the Lateral Stalk of the Complex 总被引:1,自引:0,他引:1
Valentina Giorgio Elena Bisetto Maria Eugenia Soriano Federica Dabbeni-Sala Emy Basso Valeria Petronilli Michael A. Forte Paolo Bernardi Giovanna Lippe 《The Journal of biological chemistry》2009,284(49):33982-33988
Blue native gel electrophoresis purification and immunoprecipitation of F0F1-ATP synthase from bovine heart mitochondria revealed that cyclophilin (CyP) D associates to the complex. Treatment of intact mitochondria with the membrane-permeable bifunctional reagent dimethyl 3,3-dithiobis-propionimidate (DTBP) cross-linked CyPD with the lateral stalk of ATP synthase, whereas no interactions with F1 sector subunits, the ATP synthase natural inhibitor protein IF1, and the ATP/ADP carrier were observed. The ATP synthase-CyPD interactions have functional consequences on enzyme catalysis and are modulated by phosphate (increased CyPD binding and decreased enzyme activity) and cyclosporin (Cs) A (decreased CyPD binding and increased enzyme activity). Treatment of MgATP submitochondrial particles or intact mitochondria with CsA displaced CyPD from membranes and activated both hydrolysis and synthesis of ATP sustained by the enzyme. No effect of CsA was detected in CyPD-null mitochondria, which displayed a higher specific activity of the ATP synthase than wild-type mitochondria. Modulation by CyPD binding appears to be independent of IF1, whose association to ATP synthase was not affected by CsA treatment. These findings demonstrate that CyPD association to the lateral stalk of ATP synthase modulates the activity of the complex. 相似文献
999.
This study addresses force/movement control in a dynamic “hybrid” task: the master sub-task is continuous manual tracking of a target moving along an eight-shaped Lissajous figure, with the tracking error as the primary performance index; the slave sub-task is compensation of a disturbing curl viscous field, compatibly with the primary performance index. The two sub-tasks are correlated because the lateral force the subject must exert on the eight-shape must be proportional to the longitudinal movement speed in order to perform a good tracking. The results confirm that visuo-manual tracking is characterized by an intermittent control mechanism, in agreement with previous work; the novel finding is that the overall control patterns are not altered by the presence of a large deviating force field, if compared with the undisturbed condition. It is also found that the control of interaction-forces is achieved by a combination of arm stiffness properties and direct force control, as suggested by the systematic lateral deviation of the trajectories from the nominal path and the comparison between perturbed trials and catch trials. The coordination of the two sub-tasks is quickly learnt after the activation of the deviating force field and is achieved by a combination of force and the stiffness components (about 80% vs. 20%), which is a function of the implicit accuracy of the tracking task. 相似文献
1000.