Activity and stability, effect

E.V. Kudryashova, A.K. Gladilin, A.V. Vakurov, F. Heitz, A.V. Levashov, and V.V. Mozhaev, Enzyme-poly electrolyte complexes in water-ethanol mixtures negatively charged groups artificially introduced into alpha-chymotrypsin provide additional activation and stabilization effects. Biotechnol. Bioeng. 55, 267-277 (1997). 

However, an important problem arises during the peroxidative removal of phenols from aqueous solutions PX is inactivated by free radicals, as well as by oligomeric and polymeric products formed in the reaction, which attach themselves to the enzyme (Nazari and others 2007). This suicide peroxide inactivation has been shown to reduce the sensitivity and efficiency of PX. Several techniques have been introduced to reduce the extent of suicide inactivation and to improve the lifetime of the active enzyme, such as immobilization. Moreover, Nazari and others (2007) reported a mechanism to prevent and control the suicide peroxide inactivation of horseradish PX by means of the activation and stabilization effects of Ni2+ ion, which was found to be useful in processes such as phenol removal and peroxidative conversion of reducing substrates, in which a high concentration of hydrogen peroxide may lead to irreversible enzyme inactivation. 

The present paper summarizes the current knowledge of activating and stabilizing effect of AP ions on gastrointestinal fluids, especially on main gastrointestinal enzyme - pepsin. Therefore, there is a lack of information about thermal stability of pepsin in a presence of AP ions. As the binding mechanism of AP ions on pepsin is not still clear the objective of this study is to investigate the in vitro conditions the influence of different concentrations of... 

Fig. 3.1.6 Effects of pH on the activity and stability of Cypridina luciferase (solid lines) and the quantum yield of Cypridina luciferin (dashed line). In the measurements of activity and quantum yield, luciferin (1 pg/ml) was luminesced in the presence of luciferase (a trace amount for the activity measurement 20 pg/ml for the quantum yield) in 20 mM buffer solutions of various pH containing 0.1M NaCl, at 20°C. In the stability measurement, luciferase (a trace amount) was left standing in 0.1 ml of the buffer solutions of various pH for 30 min at 20°C, then the activity was measured by adding 1 ml of 50 mM sodium phosphate buffer, pH 6.5, containing 0.1 M NaCl and 1 pg of luciferin, at 20°C. The activity and stability data are taken from Shimomura et al., 1961, with permission from John Wiley 8c Sons Ltd.

One of the key challenges for this process is dealing with the wide range of contaminants in the waste HBr stream. Both inorganic and organic contaminants may be present. These contaminants are typically reactants and products of the upstream bromination process which generated the waste HBr. In addition, they may include corrosion products of upstream equipment or ionic materials present in the water used to scrub the gaseous bromination process effluent. The main concerns about contaminants in the feed streams are their effect on catalyst activity and stability and their effect on bromine product quality. 

Solutions of surfactant-stabilized nanogels share both the advantage of gels (drastic reduction of molecular diffusion and of internal dynamics of solubilizates entrapped in the micellar aggregates) and of nonviscous liquids (nanogel-containing reversed micelles diffuse and are dispersed in a macroscopicaUy nonviscous medium). Effects on the lifetime of excited species and on the catalytic activity and stability of immobilized enzymes can be expected. 

One promising extension of this approach Is surface modification by additives and their Influence on reaction kinetics. Catalyst activity and stability under process conditions can be dramatically affected by Impurities In the feed streams ( ). Impurities (promoters) are often added to the feed Intentionally In order to selectively enhance a particular reaction channel (.9) as well as to Increase the catalyst s resistance to poisons. The selectivity and/or poison tolerance of a catalyst can often times be Improved by alloying with other metals (8,10). Although the effects of Impurities or of alloying are well recognized In catalyst formulation and utilization, little Is known about the fundamental mechanisms by which these surface modifications alter catalytic chemistry. 

Effect of pH and temperature on the purified enzyme activity and stability The conditions of the enzyme activity and the stability was done followed Buranakarl, et al. (16). 

Effect of pH and temperature on the purified enzyme activity and stability... 

CO oxidation on 1%Au supported on various metal oxide catalysts was carried out to determine the effect of metal oxide on the activity and stability of the catalysts during room temperature CO oxidation. Figure 4 shows the CO conversion as a function of time on stream on 1%Au supported on various metal oxides such as CO3O4, Fe Oj, NiO, ZrOj, and TiO. All the catalysts showed high initial CO conversions. The stability of the catalysts decreased in the following order TiO > ZrOj > NiO > FejOj > CO3O4. The stability of the catalysts appears to decrease with increasing basicity of the metal. 

Using the raw data in Fig. 3.20, we can identify the Pareto-optimal set for the HER activify/stabilify criteria. This set represents the best possible compromise between activity and stability criteria for the surface alloys that we have considered the alloys in the set are, thus, logical choices for further consideration. The presence of pure Pt on the Pareto-optimal set is, in effect, a sanity check for our computational screening procedure. Pt is well known to be the most active and stable pure metal for the HER in acidic conditions. The alloys seen on the Pareto-optimal set include RhRe and BiPt. 

The effect of biphasic mixtures on the productivity includes the contributions of solvent partitioning on enzyme activity and stability. An important activity does not necessarily lead to increased productivity. We must then distinguish between the effect of the environment on activity and productivity. 

Tzannis and Prestrelski [144,145] showed a concentration-dependent protective effect of sucrose and residual moisture on the activity and stability of tryp-sinogen during spray-drying. They found protein protection even at low carbohydrate concentrations, but they observed some destabilization at very high sucrose concentrations. They hypothesized that phase separation occurs at high sucrose concentrations, resulting in... 

Minaev, V. Z. Zaidman, N. M. Spirina, G. A., et al., Effect of Pore Structure of Alumina-Cobalt-Molybdenum Catalyst on Activity and Stability in Hydrodesulfurization of Heavy Feedstocks. Chemistry and Technology of Fuels and Oils, 1975. 11(6) pp. 436-39. 

Trends in the electronic structure of the chalcogenide catalysts have proved to be helpful in the design and understanding of the catalyst clusters. During ORR, the molecular oxygen has been found to react with the cluster as a whole, rather than individual metal atoms.177 The overall number of electrons per cluster unit (NEC) in the valence bond has been shown to have a factor in the activity and stability of the cluster catalysts.177,181 The unsubstituted Chevrel phases have a NEC of 20.177,181 Substituting or intercalating other transition metals into the crystal lattice to make ternary or pseudo-binary Chevrel phases allows for the increase of NEC. It has been found that as the NEC approaches 24, the catalytic activity improves.181 Alonso-Vante compiled the results from his previous studies to show the effect of NEC in... 

Proteases are used in many industrial areas as well as basic research. They are classified by their mechanism of catalysis. Proteases are used in the pharmacological, food and other consumer industries to convert raw materials into a final product or to alter properties of the raw material. In biomedical research, proteases are used to study the structure of other proteins and for nthesis of peptides. The choice of a protease for an application depends in part on its specificity for peptide bonds, activity and stability. Technical advances in protein engineering have enabled alteration of these properties and allowed proteases to be used more effectively. Some easily obtained proteases can be modified so that they can substitute for proteases whose supply is limited. 

Effect of Temperature and pH on Activity and Stability. When Xylanase II was subjected to the standard assay at pH 5 but at several different temperatures, the highest activity was found after incubation for 30 min at 60°C. From 21 C to 45 C the energy of activation from a linear plot of In (activity) vs. T was 41.6 2.1 kJ/mol, where the range is the standard deviation. When the standard assay was conducted at various pHs and 50°C, the highest activity was at pH 6.05. Activities half the maximum were found at pHs 4.4 and 8.0. 

Water in oil microemulsions with reverse micelles provide an interesting alternative to normal organic solvents in enzyme catalysis with hydrophobic substrates. Reverse micelles are useful microreactors because they can host proteins like enzymes. Catalytic reactions with water insoluble substrates can occur at the large internal water-oil interface inside the microemulsion. The activity and stability of biomolecules can be controlled, mainly by the concentration of water in these media. With the exact knowledge of the phase behaviom" and the corresponding activity of enzymes the application of these media can lead to favomable effects compared to aqueous systems, like hyperactivity or increased stability of the enzymes. 

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