Deactivation of enzymes

Most ultrasonic experiments are carried out in temperature controlled systems to ensure that isothermal conditions are maintained. Even a small general increase in microbial temperature can influence both the active and passive transport systems of the cell membrane/wall and this in turn may lead to an increased uptake of compounds. If the temperature is not controlled then sonication could result in a large temperature increase which will lead to the denaturation (deactivation) of enzymes, proteins and other cellular components present within the microorganism [7]. 

Case 2 Leakage through the Membrane and Deactivation of Enzyme... 

Introduction of external chemical contamination from the sampling devices into the sample should be avoided because binding of metals to biological molecules is possible in vitro, and this can change the distribution of metal-containing species in the sample. Heavy metal contaminants could cause protein precipitation as well as irreversible deactivation of enzymes. 

SC-CO2 is also becoming increasingly important as reaction media [7] for a great variety of fundamental chemical reactions ranging from catalysis to polymerization, [8,9] to synthesis and growth of inorganic materials [1,2], to nanoparticle production and preparation processes [1,2,10,11], and to biotechnological applications such as activation and deactivation of enzymes [12], biomass conversion, and biocatalysis [1,2,13],... 

Regardless of the mechanism involved, the overall result is the same. A change in receptor shape (or tertiary structure) leads eventually to the activation (or deactivation) of enzymes. Since enzymes can catalyse the reaction of a large number of molecules, there is once again an amplification of the original message such that a relatively small number of neurotransmitter molecules can lead to a biological result. 

Alternatively, the neurotransmitter/receptor interaction leads to the activation or deactivation of enzymes. In Chapter 5, this was represented as a direct process whereby the receptor and target enzyme are closely associated. In reality, the receptor and target enzyme are not directly associated and the interaction of receptor and neurotransmitter is the first step in a complex chain of events which involves several proteins and enzymes. 

Evidence of downstream effects of die drug, such as activation or deactivation of enzymes and receptors. 

Oxidation of proteins. ROS can directly oxidize free or protein-bound amino acids, leading to deactivation of enzymes (Stadtman, 1990 Stadtman and Oliver, 1991 Stadtman and Berlett, 1991). Cysteine, methionine, histidine and tryptophan are preferentially oxidized, resulting in sulfenic, sulfinic or sulfonic acids from thio-containing amino acids and in histidine- and tryptophan-endoperoxides, which subsequently degrade (Sies,... 

However, to our knowledge, most previous studies of enzyme-catalyzed polymerizations have avoided temperatures > 90 oC, which is likely due to thermal deactivation of enzyme catalyst (13-15). It has been found that enzyme immobilization can improve the stability and recyclablity of native enzyme (16). Silica particles, activated by methanesulfonic acid, are effective and economic inorganic carriers for enzyme immobilization (17). Herein, we present a minireview of our works about immobilized porcine pancareas lipase on silica particles (IPPL) for polymer synthesis, such as polycarbonates, polyesters, polyphosphates and their copoljmiers. 

Reaction Kinetics The reaction rates have been measured at pH = 7.8 and T 37° C, using a 5% Pen G substrate concentration. Titration with 0.1 molar NaOH has been used to determine the amount of product formation. The values of free and immobilized cells have been obtained from the Llneweaver-Burk plots as shown for some examples in Figure 5. Following to irreversible deactivation of enzymes during the process of immobilization, the inequality X nnnobil holds. The following approach has been developed for... 

Aymard C, Belarbi A (2000) Kinetics of thermal deactivation of enzymes a simple three parameters phenomenological model can describe the decay of enzyme activity, irrespectively of the mechanism. Enzyme Microb Technol 27(8) 612-618... 

When the spray-drying operation is cocurrent, i.e., hot air introduced into the dryer close to the atomizing device, there is less danger of overheating as the evaporation rates are high (34-160 kg/h/m of particle area) [3], Thus, cocurrent drying chambers are preferred to minimize heat deactivation of enzymes during the process. 

Ascorbic acid is involved in removal of active oxygen during photosynthesis, with activation and deactivation of enzymes, mobilization of ferrous ion, growth regulation, and the oxidation of organic compounds. One well-known exam-... 

There are two major difficulties in the integration of a biological reaction with pervaporation the difficulty of operating at a relatively high temperature to avoid the thermal death of the microorganisms or the deactivation of enzymes, and the (bio-)fouling effect of the fermentation broth on the... 

The exact mechanism of antifungal activity is still unknown, and is currently the subject of many researches. There is three suggested qualitative concepts DNA association, cell wall damage and deactivation of enzymes. On the molecular level it is known that silver is enable to form a bond with S, N, and O atoms, and also to catalyze the formation of disulfide bonds. 

Enzymes are fragile. Modifying the enzyme environment (temperature, pH, ionic strength, solvent, surfactant, and so forth—see below) usually leads to an alteration of the enzyme structure, with an immediate loss of its activity. In the presence of proteases, the deactivation of enzymes may also result from another mechanism—autodigestion. 

Fig. 4 Effect of PEG hindrance on enzyme active site access. The high steric hindrance of branched PEG may explain the lower deactivation of enzymes as compared to linear PEGS of the same size...

Phosphorylation is a process involved in many cellular pathways such as activation or deactivation of enzymes. An extensive study of enantioselective phosphorylation reactions was reported by Miller and coworkers using several 7i-(Me)-histidine containing peptides. The proposed catalytic cycle involves the generation of an high energy phospho-imidazoUum ion and its reaction with the alcohol substrate in a site-specific manner. Following this mechanism, regio- and enantiopure phosphorylated alcohols can be prepared (Scheme 5.8). 

Fig. 9.54 Deactivation of enzymes by protein unfolding. (From https //upload.wikimedia.orgfyirikipedia/ commons/ /I d/Process of Denaturation.svg).

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