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Deactivation of the enzyme

The economics of an immobilised cell process depend on the lifetime of the microorganism and a continued level of clean product delivered by the fixed cells. It is important to eliminate the free cells from the downstream product without the use of any units such as centrifuge or filtration processes. Since the cells are retained in the ICR, the activity of intracellular enzymes may play a major role. It is assumed that the deactivation of the enzyme at constant temperature follows a first-order equation as shown below 17... [Pg.218]

In contrast to enzyme- and base-catalyzed DKRs, there are only a few reports of enzyme- and acid-catalyzed DKRs. A plausible explanation is that deactivation of the enzyme can occur under acidic conditions. Also, decomposition of the substrate has... [Pg.101]

In this context the lipase was immobilized on a support which also adsorbed water and propionic acid. During the reaction, the water caused a decrease of the reaction rate. While the water adsorption on the catalyst results in a reversible decrease of the enzyme activity, an excessive accumulation of water in the bulk mobile phase resulted in rapid irreversible deactivation of the enzyme. [Pg.201]

Aliphatic ethers with branched side chains such as MTBE (methyl t-butyl ether), especially, deactivate enzymes only to a very small degree in incubation experiments for example, the BAL mentioned above has a half-life h/2 of up to 500 h in aqueous-organic two-phase systems (see Fig. 3.1.6) [21]. This may not hold true for a special enzyme/solvent combination under process conditions. When incubated at higher temperatures or even in the presence of the substrate benzaldehyde the deactivation of the enzyme is much higher (see Table 3.1.2)... [Pg.423]

The amount of DERA that has to be added for the production of (3R,5S)-6-chloro-2,4,6-trideoxyhexapyranoside (1) is significant, which can clearly be attributed to the rapid deactivation of the enzyme during reaction, arising from substrates and the reaction products. The Km value of DERA for CLAA at saturating acetaldehyde... [Pg.138]

The temperature effect is much more significant than the pressure effect. For the enzyme stability, a temperature increase above certain levels, depending on the enzyme, results in deactivation of the enzyme. In Table 9.2-2, the residual activities of various enzymes after one hour incubation time, in supercritical CO2 at 150 bar, are given. It is obvious that temperatures over ca. 75°C reduce enzyme activity dramatically. However, no correlation for the stability with the temperature for different types of enzymes is yet available [8-10],... [Pg.488]

Carboxymethylation. It was found by Vallee and Li that one cysteine residue per subunit may be selectively carboxymethylated with iodoacetate.1405 Since this reaction causes deactivation of the enzyme, this cysteine residue, later identified as Cys-46,1406 was suggested to be at the active site. The deactivated carboxymethylated enzyme still binds NAD+. The carboxymethylation of this residue is preceded by a reversible binding of iodoacetate to the enzyme.1407 This observation has helped to identify an anion-binding site in the coenzymebinding domain, where the pyrophosphate group of the coenzyme binds. [Pg.1015]

Deactivation of the enzyme catalyst often goes unnoticed, especially if the biocatalyst is fairly stable and/or the time of observation is short, such as during an initial rate measurement. If we analyze the short-time behavior of Eq. (17.23) we can replace the exponential by a linear term deviating from unity. At short times, exp (-kd obs t) 1 - kdobs t, and Eq. (17.24) is recovered. [Pg.495]

It is assumed that deactivation of the enzyme occurs according to first-order kinetics (Eq. (19.7)). [Pg.542]

The definition of a more efficient enzymatic system could be based on the separation of the catalytic cycle of the enzyme and the degradation step by the Mn3+ reactive species in MnP systems. The Mn3+-chelates present several advantages in their use as oxidants. They are more tolerant to protein denaturing conditions such as extremes of temperature, pH, oxidants, organic solvents, detergents, and proteases, and they are smaller than proteins therefore, they can penetrate microporous barriers inaccessible to proteins. The optimization of the production of the Mn3+-chelate will have to be compatible with the minimal consumption and deactivation of the enzyme. [Pg.275]

Abstract Peroxidases use H2O2 as electron acceptor in order to catalyze a variety of oxidative reactions through a catalytic cycle with two intermediates. Additionally to these intermediates, a third species (Compound III) is produced when ferric peroxidases are exposed to an excess of H2O2. Compound III is a peroxy-Fe111 porphyrin free radical, the best described of the intermediates leading to the irreversible deactivation of the enzymes. This chapter aims to describe the structure, stability, formation, and decay of Compound III as fundamental knowledge required to understand, and potentially to control, the peroxidases H202-dependent deactivation process. [Pg.291]

In summary, it is generally assumed that regulation of C4 photosynthesis involves most of the mechanisms discussed earlier for C, photosynthesis. There are, however, a number of specializations in the light-dark activation and deactivation of the enzymes involved in the initial fixation of CO2 in the mesophyll and its release in the bundle sheath. Additional controls are required for the enzymes metabolizing compounds which travel down diffusion gradients between the cell types. [Pg.193]

All the transformations carried out with penicillin acylase and employing phenylacetates or -amides as substrates are hampered by the very limited solubility of these esters in aqueous environments. Although the enzyme tolerates considerable amounts of organic cosolvents, generally their application results in at least a partial deactivation of the enzyme. Since penicillin acylase accepts variations in the phenylacetic acid part of its substrates, pyridyl acetic acid esters were employed to enhance the solubihty of the substrates in aqueous solution. In fact, several simple 4-pyridylacetates turned out to be fairly soluble in aqueous media and were attacked at very acceptable rates by the enzyme [ 19 ]. It is interesting to note that the velocity of the enzymatic transformations depends... [Pg.72]

The region of the enzyme that interacts with substrates is referred to as the active site. For reaction to occur there must be an appropriate fit between the three-dimensional structure of this site and the geometry of the reactant molecule so that an enzyme-substrate complex may form (Emil Fischer s lock and key hypothesis). Enzymes are relatively labile species and when subjected to unfavorable conditions of temperature, pH, pressure, chemical environment, etc., they can lose their catalytic activity. In these situations, deactivation of the enzyme can usually be attributed to changes in the geometric configuration of the active site. [Pg.1367]

Inertness with respect to both the enzyme-mediated reactions of interest and reactions leading to deactivation of the enzyme. [Pg.1368]

Thus, with reference to lipase, it seems that loss of water molecules from the microenvironment of the enzyme structure may not be the key for destabilization or deactivation of the enzyme since lipase is fairly stable under anhydrous condition. However, H-bonding nature of the component ions of ILs might be important for maintaining the integrity of the native conformation of the enzyme. At the same time, too strong H-bond could be detrimental due to the disruption of key H-bonds responsible for maintaining native structure which leads to the collapse of the protein framework or unfolding of the protein. [Pg.244]

Thus, the active functions of the carrier material, which is usuaUy a naturally occurring or synthetically prepared polymer, can be of almost any nature. Introduction of the spacer molecules (functionalisation) is also dte phase determining the activity of the immobilised enzyme preparation the more spacer molecules per unit area, the more enzyme molecules can be attached. Of course, steric hindrance exerts a limit on dtis number. After the carrier has been functionalised, excess reagent is removed by hltration and washing and the enzyme can be attached to the support The immobilised enzyme thus obtained is usually stored in an aqueous medium in ordra to avoid dehydration, which may lead to irreversible deactivation of the enzyme. Just before use, die beads containing the enzyme are collected by filtration, wash, and added to the aqueous solution of substrate. Once tl desired conversion has been ediected, die beads are removed by dltration, washed, and either stored or reused direcdy afterwards. [Pg.172]

Hollow-fiber membrane reactors with immobilized lipases have been used for the continuous hydrolysis of triglycerides188 and in the esterification of fatty acids.189 There was no deactivation of the enzyme in the former case in 16 days. In a comparable run in solution, the enzyme lost 80% of its activity in 2 days of operation. The latter case used dodecanol and decanoic acid in hexane to give the ester in 97% yield. The half-life of the immobilized enzyme was 70 days. The integration of reaction and separation can decrease product inhibition, increase selectivity, shift equilibria, and reduce the number of downstream operations.190... [Pg.252]

Also known as iditol dehydrogenase, this enzyme catalyzes the interconversion of sorhitol to fructose in the presence of the coenzyme nicotinamide adenine dinucleotide. The enzyme is cytosolic, with the highest tissue concentration in the liver and a short half-life of less than a few hours. The plasma enzyme is relatively unstable and activity can he rapidly lost when serum is stored at room temperature storage at lower temperatures reduces the deactivation of the enzyme. The enzyme measurement can he useful in canine, nonhuman primate, and rat studies as a conhrmatory test for hepatotoxicity (Dooley, Turnquist, and Racich 1979 Pakuts, Whitehouse, and Paul 1988 Blazka et al. 1996 Travlos et al. 1996). However, the changes in liver injury are often relatively small compared to baseline values. [Pg.28]

As previously mentioned, part of our work was dedicated to the study of bio-activity of the enzyme used to prepare bioartificial hydrogels the enzyme activity was monitored, in a phosphate buffer containing starch substrate (0.2 mg/ml), by measuring the substrate concentration remaining in the batch solution at different times. The results, compared with free a-amylase behaviour, indicated that the catalytic hydrolysis of starch was the same for free a-amylase and a-amylase delivered from bioartificial blend no deactivation of the enzyme because of the presence of PVA was observed either in solution or after the preparation through casting procedure. On the contrary, a-amylase seemed slightly more stable in the polymer network. [Pg.55]


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See also in sourсe #XX -- [ Pg.343 ]




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