Non-essential activation of pepsin by Al3+ “in vitro”

The in vitro effect of Al3+ ions on pepsin activity at pH 2, via kinetic parameters was evaluated. Kinetic study showed that Al3+ ions increase the maximal velocity (Vmax) rather than apparent affinity for substrate (KS) implying the non-competitive nature of activation which indicated that aluminium was a non-essential activator of partial non-competitive type.Physical chemistry 2008 : 9th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 200

Microwawe irradiation influence on enzyme kinetics

Kinetic study of microwave (MW) irradiated enzyme pepsin was performed. Decreased enzyme activity was observed, under constant temperature and absorbed MW energy per time unit. In accordance with experimental conditions, Vmax and Km were calculated for irradiated pepsin solutions and compared with control reaction with non-irradiated pepsin.Physical chemistry 2008 : 9th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 200

Temperature and Al3+ influence on electrophoretic mobility of porcine pepsin

The influence of temperature and different concentrations of Al3+ on pepsin electrophoretic mobility was investigated. The increase of Al3+ concentrations causes the decrease the electrophoretic mobility of enzyme. Also the increase of temperature induced the same effect. The influence of both temperature and Al3+ ion concentrations is additive.Physical chemistry 2006 : 8th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-29 September 200

Kinetics of heat denaturation of pepsin in a strong acid media

Heat aggregation of pepsin, in a strong acid media; involve the stage of nucleation, and the stage of growth of aggregates. The initial parts of the kinetic curves of aggregation were followed via monitoring the increase of absorbance (A) and were linearized as {dA/dt; t} and {A; t 2 } functions. The slope of these curves is proportional to the product rate constant of reversible denaturation and the rate constant of growth of aggregates. Addition of Al3+ ions display a lag period whose appearance is caused by intramolecular predenaturational changes in the pepsin molecule.Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 200

Spectrophotometric study of solution equilibria between Al3+ ion and L-histidine

Aluminium(III) ion and L-histidine (HHis) react in water solution to yield two mononuclear binary complexes [Al(HHis)]3+ and [Al(HHis)His] 2+. The over-all stability constants for these complexes were calculated by non-linearleast-squarestreatment of the spectrophotometric data and found to be: log β1,1,1 = 13.12 ± 0.04, log β1,2,1 = 20.9 ± 0.1, respectively. Indices refer to stoichiometric coefficients in complexation equilibrium: p Al + q His + r H → [AlpHisqHr]. The possible structures of the complexes in solution, are discussed.Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 200

The influence of Al3+ion on porcine pepsin activity in vitro

The in vitro effect of Al3+ ions in the concentration range 1.710-6M-8.710-3M on pepsin activity at pH 2, via kinetic parameters and its electrophoretic mobility was evaluated. Kinetic study demonstrated the existence of an activation effect of Al3+ at pH 2 on pepsin molecule. Kinetic analysis with respect to concentrations of haemoglobin showed that Al3+ ions increase the maximal velocity (Vmax) and kcat values rather than apparent affinity for substrate (KS) implying the non-competitive nature of activation which indicated that aluminium was a non-essential activator of partial non-competitive type. The values of the equilibrium constants KS and KmA for dissociation of corresponding complexes were evaluated as 0.9040.083mM and 8.560.51M, respectively. Dissociation constant KA, of activator from enzyme-activator complex calculated via kinetic and direct measurement of Al3+ binding data, as well as activation constant A50, the activator concentration that gives a rate equal to half at a saturating concentration of activator, were found to be 8.820.90M, 8.390.76M, and 8.050.48M respectively. Native PAGE electrophoresis shows the decrease in electrophoretic mobility of pepsin and confirms modification of the electric charge and conformational changes of pepsin caused by bound Al3+ on the pepsin molecule. Al3+ induced conformational changes of pepsin were verified by UV-VIS and IR spectra. Moreover, the absence of conformational changes in the haemoglobin molecule in the presence of Al3+ ions confirms that the obtained activation is a consequence of conformational changes caused only in the pepsin molecule

Analysis of thermal denaturation of pepsin on basis of MALDI-TOF MS and PAGE experimental data

To obtain detailed information about properties of pepsin in thermal denaturing conditions, polyacrylamide gel electrophoresis (PAGE) and matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS) experimental data were analyzed. These methods were used to analyze the changes in the structural properties of pepsin molecule subjected to broad-range temperature variations, from 25 ºC to 70 ºC, and pH range from 1 to 4.Physical chemistry 2012 : 11th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 201

Controlled Colloidal Synthesis and Basic Electrochemical Properties of TiO2-Supported Pt

TiO2 was synthesized by forced hydrolysis process in order to be used as the support for Pt electrocatalyst (Pt/TiO2). Pt was deposited from Pt colloid solution synthesized by microwave-assisted polyol process. TiO2 powder (or C) was dispersed into H2O and 2 M H2SO4. The obtained suspension was stirred and Pt colloid was added afterwards. Upon filtration and rinsing with water, the obtained Pt/TiO2 (or Pt/C) catalyst was thermally treated at 160 C in N2 atmosphere. The catalyst water suspension for the preparation of 0.31 mg/cm2 thin layer electrode was loaded onto glassy carbon disk. Physical and chemical properties of the TiO2 and supported Pt catalyst were characterized by EDS, SEM, dynamic light scattering and XRD techniques. The influence of TiO2 thermal treatment on the electrochemical properties of Pt/TiO2 was also checked. Nominal Pt loading was 20 wt. %. EDS method revealed 18 wt. % loading of Pt on TiO2. The electrochemical properties of the Pt/TiO2 were examined by cyclic voltammetry in 0.1 M HClO4. The obtained results were compared with those obtained for carbon-supported Pt under the same conditions (Figure 1). The charge corresponding to the hydrogen desorption on Pt/TiO2 is lower than expected for 20 wt. % Pt. Although the voltammetric response is typical for Pt-based electrode material, the charge corresponds only to ~3 wt. % Pt. SEM images showed that TiO2 particles tend to form 3μm-sized agglomerates of ellipsoidal shape. The results indicate the possibility for platinum particles to be trapped inside TiO2 agglomerates. Even though calcination of TiO2 improved the Pt uptake from colloidal dispersion, it is still not as effective as commercial carbon support.June 07-11, 2015, Pravets, Bulgari

Application of Peleg Model on Mass Transfer Kinetics During Osmotic Dehydratation of Pear Cubes in Sucrose Solution

The applicability of Peleg model was investigated for predicting mass transfer kinetics during the osmotic dehydration (OD) process of pears, at different concentrations (40, 60 and 70%, w/w) and temperatures (20, 35 and 50 degrees C) of sucrose solution. Increase in sucrose solution concentration resulted in higher water loss (WL) and solid gain (SG) values through the osmotic treatment period. After 360 min of osmotic treatment of pears, WL ranged from 23.71 to 31.68% at 20 degrees C, from 24.80 to 40.38% at 35 degrees C and from 33.30 to 52.07% at 50 degrees C of initial weight of pears. The increase of dry mass of the samples, SG, after 360 min of osmotic treatment ranged from 3.02 to 6.68% at 20 degrees C, from 4.15 to 7.71% at 35 degrees C and from 5.00 to 8.92% at 50 degrees C. Pelegs rate constants, k(1)(WL) and k(1)(SG), decreased with increasing temperature, as well as decreased with increasing concentration of osmotic solution at constant temperature. Both capacity constants k(2)(WL) and k(2)(SG) also exhibited the inverse relationship between capacity constant and temperature, as well as concentration of the osmotic solution. Pelegs rate constants for WL and SG at all temperatures followed an Arrhenius type relationship. The predicted equilibrium values were very close to experimental ones, which was confirmed with high coefficients of determination and by the residual analysis