1,354,461 research outputs found
Esterolytic properties of leucine-proteinase, the leucine-specific serine proteinase from spinach (Spinacia oleracea L.)
No full textSteady-state and pre-steady-state kinetics for the hydrolysis of p-nitrophenyl esters of N-alpha-carbobenzoxy(-l-)amino acids catalyzed by leucine-proteinase were determined between pH 5 and 10 (I = 0.1 molar) at 23 +/- 0.5 degrees C. For the substrates considered: (a) the acylation step is rate-limiting in catalysis; (b) the pH profiles of k(cat) and k(cat)/K(m) reflect the ionization of two groups with pK(a) values ranging between 6.5 and 6.9, and 8.1 and 8.3 (probably, the histidine residue involved in the catalytic triad and the N-terminus, respectively); and (c) values of K(m) are pH independent. Among the substrates examined, N-alpha-carbobenzoxy-l-leucine-p-nitrophenyl ester shows the most favorable catalytic parameters and allows to determine an enzyme concentration as low as 5 x 10(-10) molar at the optimum pH value (approximately 7.5)
An hydraulic monitoring system on a Bridge over river Esino, Italy
No full textBridge pier scour (Ballio and Orsi, 2001) is one of the most common causes of bridge collapses.
The most critical situation is the flood condition, when pier scour depth can become high and its
time-evolution is relatively fast. As available models are unable to predict scour development with
sufficient accuracy, several methods have been developed allowing for in situ scour measurements
(Lin et al, 2005 and De Falco and Mele, 2002). The application case of this work is the Scisciano
Bridge (Province of Ancona, Italy) on the Esino River, partially collapsed during the flood in 1990
by local scour erosion. Nowadays this newly built bridge is in a crucial position because it connects
two Loccioni Group buildings. Inside the Flumen project, sponsored by Loccioni, a monitoring
system is being developed to manage the bridge during floods
Turbulent stresses at the bottom surface near an abutment: a laboratory-scale numerical experiment
No full textThe flow field around a bridge abutment is analyzed by means of large eddy simulation. The geometrical configuration corresponds to the initial condition of a scour process (flat bed). The three-dimensional flow structure in front of the abutment is analyzed with special emphasis on its effects on shear stresses and pressure gradients on the bottom wall which, in turn, are discussed with respect to their potential scouring action. Both first- and second-order statistics around the abutment are quantitatively discussed, together with probability density distributions of stresses in specific locations. The investigation shows that several terms may play a relevant role in
sediment transport around the obstacle. Specifically, the mean horizontal pressure gradient may reach values as large as two orders of magnitude that of a canonical boundary layer, whereas the instantaneous vertical pressure gradient may give an uplifting force comparable to the immersed weight of the sediment. The analysis suggests that local scour models should incorporate the contribution to the destabilizing force coming from pressure stresses and from turbulent fluctuations
Purification and Characterization of Leu-Proteinase, the Leucine Specific Serine Proteinase from Spinach (Spinacia oleracea L.) Leaves
No full textThe leucine specific serine proteinase present in the soluble fraction of leaves from Spinacia oleracea L. (called Leu-proteinase) has been purified by acetone precipitation and a combination of gel-filtration, ion exchange, and adsorption chromatography. This enzyme shows a molecular weight of 60,000 +/- 3,000 daltons, an isoelectric point of 4.8 +/- 0.1, and a relative electrophoretic mobility of 0.58 +/- 0.03. The Leu-proteinase catalyzed hydrolysis of p-nitroanilides of N-alpha-substituted(-l-)amino acids as well as of chromogenic macromolecular substrates has been investigated between pH 5 and 10 at 23 +/- 0.5 degrees C and I = 0.1 molar. The enzyme activity is characterized by a bell-shaped profile with an optimum pH value around 7.5, reflecting the acid-base equilibrium of groups with pK(a) values of 6.8 +/- 0.1 and 8.2 +/- 0.1 (possibly the histidyl residue present at the active site of the enzyme and the N-terminus group). Among the substrates considered, N-alpha-benzoyl-l-leucine p-nitroanilide shows the most favorable catalytic parameters and allows to determine an enzyme concentration as low as 1 x 10(-9) molar. In agreement with the enzyme specificity, only N-alpha-tosyl-l-leucine chloromethyl ketone, di-isopropyl fluorophosphate and phenylmethylsulfonyl fluoride, among compounds considered specific for serine enzymes, strongly inhibit the Leu-proteinase. Accordingly, the enzyme activity is insensitive to cations, chelating agents, sulfydryl group reagents, and activators
Biological activities of pseudomycin A, a lipodepsinonapeptide from Pseudomonas syringae MSU 16H
No full textSimilarly to other Pseudomonas lipodepsinonapeptides, pseudomycin A inhibits proton extrusion from maize roots, promotes closure of stomata in Vicia faba, necrosis of tobacco leaves, haemolysis of human erythrocytes, affects H(+)-ATPase activity and proton translocation in plasma membrane vesicles, and stimulates succinate respiration in pea mitochondria. In general, the biological activities of pseudomycin A are lower than those of syringomycin-E, the prototype member of this family of bacterial metabolities. This difference might depend on the diverse number and distribution of charged residues in the peptide moiety of these compounds
Toxins of Pseudomonas syringae pv. syringae affect H+-transport across the plasma membrane of maize
No full textFeasibility analysis of a movable bridge compensating for clearance deficit during floods
No full textThis paper deals with the problem of mountain river crossing in old towns whose urban morphology often prevents one from building a ramp to access the bridge. If this is the case, the proposed solution consists in designing a bridge which can be lifted when a flood occurs. Some bridges of this kind are actually on duty in the Italian Alps but all of them are moved by means of hydraulic jacks.
A table bridge moved by the buoyancy force of the river water is suggested. The design concept is here specified for a real case where a floating bridge is placed in the position where a bridge moved by hydraulic jacks was built. This choice enables one to compare the two solutions under the same conditions.
The simplicity and robustness of the design, as well as the possibility of fully automatic functioning without any external support (i.e. electric energy) lead the authors to state that the floating bridge suggested is preferable to a bridge lifted by means of hydraulic jacks
Turbulent stresses at the bottom surface near an abutment: a laboratory-scale numerical experiment
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