1,720,975 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
Effect of polyols and sugars on heat-induced flavin dissociation in glucose oxidase
No full textA thermodynamic investigation was carried out on heat-induced flavin dissociation in Aspergillus niger glucose oxidase. Experimental measurements performed by difference spectroscopy showed that the dissociation of the FAD cofactors is a highly cooperative process and is probably related to the extended conformational changes resulting from protein unfolding. Microenvironmental modifications attained by the addition of polyhydric compounds (glycerol, fructose, sucrose and sorbitol) from 10 to 30% by weight were found to hinder the dissociation. The stabilizing effect provided by these substances was interpreted as a consequence of preferential exclusion phenomena, which are likely to be determined by the perturbation of the surface tension of water, in the case of sugars, or by the solvophobic effect, in the case of glycerol
Carrier-mediated transport phenomena in enzyme-loaded liposomes
No full textA mathematical model which describes the kinetic behaviour of enzyme- loaded liposomes containing a substrate transporter in the lipid bilayer is presented. The model accounts for the facilitated diffusion across the membrane and the chemical reaction in the aqueous core. Both steady-state and transient kinetics are analysed. The model allows to quantify the influence of transport phenomena on the catalytic properties of the microencapsulated enzyme and provides some directions for the design of an artificial vesicle in which a selective substrate carrier has been included
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
Analysis of the kinetic bahaviour of engineered liposomes for biotechnological applications
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