1,721,101 research outputs found
Urease-loaded liposomes as detoxifying microreactors: Effect of ammonia accumulation on enzyme kinetics
No full textA kinetic model was developed which describes the unsteady behaviour of liposomes entrapping the enzyme urease. The model allows to determine how the reactant concentrations, the internal pH and the catalytically active enzyme fraction vary with time. A numerical simulation carried out to elucidate the effects of the buffer pH and ionic strength on the active enzyme decay provided useful directions for the selection of the operating conditions to be used for the removal of urea by urease-loaded liposomes
Enhanced lycopene recovery from tomato processing waste by enzymatic degradation of plant tissue components
Full text linkEight commercial enzyme preparations with pectinolytic, cellulolytic, hemicellulolytic and proteolytic activities were tested for their ability to enhance lycopene extraction from tomato peels. Screening experiments were performed at 40 °C by subjecting the peels to a 1-h enzyme
incubation followed by 1-h hexane extraction. The resulting yields were between 51 and 195.9 mg of lycopene per 100 g of dry tomato peels, while the value obtained for the untreated peels was 23.7 mg /100 g. Synergistic and antagonist effects were observed when different enzyme products
were used in 50:50 (v/v) combination. The preparations richest in cellulase and pectinase were the most efficient, with an up to 10-fold increase in extraction yield. A statistical analysis of factors affecting lycopene extraction revealed that enzyme dosage was the most influential,
followed by temperature and enzyme incubation time. A strong interaction was also found between the latter two variables
MILD ENZYMATIC METHOD FOR THE EXTRACTION OF LYCOPENE FROM TOMATO PASTE
Full text linkFour commercial enzyme preparations containing cell-wall degrading enzyme activities were tested for their ability to facilitate lycopene extraction from tomato paste. At 25 degrees C, up to 75.6% of the lycopene present in the tomato product was extracted by a two-stage procedure that consisted of a preliminary 5 hour enzyme incubation followed by a 3 hour solvent (hexane or ethyl acetate) extraction. Increasing the duration of the enzymatic treatment to 12-18 h allowed the recovery of 85-90% of total lycopene. The highest extraction yields were achieved by using enzyme preparations' with polygalacturonase and pectin methylesterase in addition to pectin lyase or cellulase activities
Experimental study on the interaction between lead and serum albumin
No full textThe interaction between lead (Pb 2+) and bovine serum albumin (BSA) was studied in the temperature range of 10-40 °C through metal-titration experiments under equilibrium conditions. Lead binding to BSA was monitored by measuring the intensity changes in the difference absorption band at 243 nm following the addition of increasing amounts of lead ions to an aqueous solution at constant protein concentration (2.5 × 10 -5 M). The equilibrium binding data were found to be well described by a Langmuir-type equation, with an almost temperature-independent saturation value. According to the estimated δH 0 and δS 0, the binding of Pb 2+ to BSA was both enthalpy-driven and entropy-driven, with the entropic contribution providing the major driving force. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd
Effect of Trehalose on Thermal Stability of Bovine Serum Albumin
Full text linkTrehalose at 10-30% (w/w) greatly stabilized bovine serum albumin (BSA) against thermal denaturation. The highest stabilization was reached in 30% trehalose at 65 degrees C, when the protein's half life was increased from 72 to 335 min. A kinetic analysis based on the Lumry-Eyring mechanism of inactivation showed that BSA denaturation can be described by a first-order rate expression with an apparent activation energy ranging from 238.1 to 246.4 kJ mol(-1)
Chloramphenicol removal from wastewater by UV/H2O2 advanced oxidation process
No full textThe efficacy of the UV-H2O2 treatment to degrade the antibioticchloramphenicol (CHL) was investigated at 20°C using a low-pressure mercury lamp as UV source. A two-level factorial design was used to study the effects of initial CHL(c0 = 40-80 mg L-1) and H2O2(h0 = 20-50mM) concentrations, reaction time (t = 30-70 min) and irradiance level (I = 400-800 μW cm-2) on CHLdegradation. Under the best conditions (c0 = 40 mg L-1, h0 = 20 mM, t = 70 min, I = 800 μW cm-2), almost 96% of the antibiotic was degraded. No residual antibiotic activity was detected in the treated solution, thereby confirming the efficacy of the UV-H2O2 process. © (2013) Trans Tech Publications, Switzerland
Thermostabilization of proteins by water-miscible additives
No full textStabilization of protein structure by solvent components is st simple and effective strategy for preserving protein activity under adverse thermal conditions. Glycerol, sugars and some inorganic salts have been known for a long time to hinder protein deactivation when added in high concentrations (> 1 mol L-1). Detailed mechanisms of their action, however, were only partly clarified and empirical protocols are generally followed to accomplish stabilization. This paper is intended to provide a brief survey on the principles of protein stabilization by water-miscible additives. The molecular aspects of stabilization are first analysed, particularly in the light of preferential hydration phenomena. Attention is focused then on the theoretical modeling of solvent effects. The models examined include the solvophobic theory and a molecular-thermodynamic model recently developed by the authors. Evidence emerging from the literature dearly indicates that the complexity of the problem in question prevents a comprehensive rationalization of the influence of additives on stability. Nonetheless some guidelines can be derived that could be beneficial for proper formulation of the media containing stabilizing components
Molecular thermodynamics of heat-induced protein unfolding in aqueous media
No full textThe molecular thermodynamic model studied is based on the two-state mechanism of inactivation, in which only native folded and polymorphous unfolded protein forms are present at equilibrium. The influence of solvent on protein stability is described in terms of perturbation of the protein distribution between the two conformational states. An expression derived for the chemical potential of the protein accounts for conformational changes, ideal mixing effects, and interaction of the protein with the surrounding medium. Thermal unfolding of lysozyme was then studied in the absence or presence of hydroxylic compounds. Ultraviolet difference spectroscopy was used to monitor the conformational changes induced by heating and to determine the melting temperature of the protein. The additives investigated are ethanol, glycols, and natural osmolytes. Media containing ethanol and glycols destabilized lysozyme, whereas sugars increased the conformational stability of the protein. For all of the systems examined the melting temperature was linearly related to the surface tension of the mired solvent, supporting the ability of the model to describe the influence of the solvent and composition on lysozyme unfolding. Model predictions agreed fairly well with published differential scanning calorimetric data. The influence of hydroxylic additives on protein's conformational stability does not extend to any special property of these components, but to their ability to perturb the surface tension of water. This model can be used to interpret and correlate thermal unfolding data and to solve the problem of protein stabilization
- …
