Enzyme desorption

COOH groups of the PE (PAA or PGA) and the -NH2 moieties of the pre-loaded protein, using l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) as a catalyst [99]. Negligible enzyme desorption (<0.1 %) is observed from cross-linked lysozyme-loaded MS spheres after exposing the samples to an aqueous solution for 48 h, while about 25 % of the immobilized lysozyme is desorbed under the same conditions when the lysozyme is not cross-linked. 

Table 1 shows that some Dowex/invertase complexes, in which the resins used were 1x2-200, 1x4-50, 1x4-100, 1x4-200, 1x8-50, and 1x8-200, retained 100% of protein molecules during sucrose hydrolysis. The absence of enzyme desorption from the support enhances the half-life of the immobilized complex when employed in repeated-batch or continuous processes (18). 

Immobilization by adsorption. This is the simplest method and consists in enzyme adsorption due to electrostatic, hydrophobic or dispersive forces on the electrode surface. The disadvantage is the high probability of enzyme desorption and denaturing. 

Solvent compatibility Swelling, dissolution of carrier, enzyme desorption, controlled dissolution... 

More complicated immobilization methods have been described, including covalent attachment to a support, entrapment inside particles (such as silica made by a sol-gel process), and covalent incorporation into polymer particles ( biocatalytic plastics ). However, it is not clear that any of these methods is superior to simple adsorption, particularly for use in low-water media, where enzyme desorption is not an issue. 

Desorption The procedure of evaluation of enzyme desorption flom the carrier was as follows after incubating the enzyme with the carrier in corresponding conditions, the suspension was centrifuged. The precipitate was then washed by buffer solution and centrifuged once more. This procedure was repeated three times by tenfold quantity of the buffer. Then, we joined all the portions of supernatants after whieh, we measured the activity of the immobilized enzyme and the activity of the supernatant. We have also measured preliminarily the activity of the enzyme solution that was used for immobilization. Based on the correlation between activities, we calculated the level of desorption of the enzyme from the carrier. 

The results indicate that acetylation of the enzyme considerably improves immobilization stability of the process. Acetylation of the enzyme reduces enzyme desorption resulting... 

Reusability of immobilized CALB was tested in subsequent cycles of methyl butyrate hydrolysis. It can be observed in Fig. 7 that CALB-7A retained less than 50% of its initial hydrolytic activity after the third cycle of reaction whereas Novozyme 435 retained almost 70% after the tenth cycle (Fig. 7). Other authors [36] observed that CALB immobilized on activated carbon retained more than 55% of its initial activity after the sixth cycle of methyl butyrate hydrolysis. The worse operational stability of CALB immobilized on coconut fiber, when compared to CALB immobilized on activated carbon and to Novozyme 435, may be due to enzyme desorption during reaction, induced by the hydrophobic substrate, and by the low enzyme load adsorbed. As discussed before, the driven forces of CALB adsorption on coconut fiber are electrostatic interactions that are weaker than hydrophobic interactions, which predominate on Novozyme 435 and CALB adsorbed on activated carbon. Furthermore, both aetivated carbon and the resin used in the preparation of Novozyme 435 are porous support with high superficial area available for enzyme immobilization, allowing obtaining of high enzyme load. Coconut fiber, on the other hand, does not have a porous structure, and it has a low surface area [27], making it difficult to achieve high enzyme loads. 

To establish the operational stability over longer periods of operation, enzyme activity in the treated juice and wine was analysed. It was found that there is no enzyme desorption up to a monitoring period of 5 repeated batches and that 100% of activity is retained. In addition, after 6 months of storage at +4°C, the activity of the immobilized B-glucosidase was 100 % of the original activity. 

Laser desorption methods are particularly useful for substances of high mass such as natural and synthetic polymers. Glycosides, proteins, large peptides, enzymes, paints, ceramics, bone, and large... 

The steady structure determined by the value of Kw (Fig. 1) for the entire class of carboxylic CP obtained by precipitation copolymerization is one of the most important factors determining the possibility of reversible bonding of proteins absorbed by carboxylic CP with a high sorption capacity [16,19]. Thus, for the MA-HHTT system (Fig. 2), a complete desorption of enzyme is carried out on crosslinked copolymers characterized by low Kw values. In crosslinked structures exhibiting looser structure (Kw P 1), owing to the mobility of chain fragments of CP especially in the process of desorption, the macromolecules of sorbed protein are irreversibly captured as a result of a marked polyfunctional interaction. 

Figure 15.4(A) shows the effect of the R = Zn2+/Al3+ ratio, which determines the charge density of the LDH layer, on the Freundlich adsorption isotherms. K values are far higher than those measured for smectite or other inorganic matrices. The increase in Kf with the charge density (Kf= 215, 228, 325mg/g, respectively, for R = 4, 3 and 2) is supported by a mechanism of adsorption based on an anion exchange reaction. The desorption isotherms confirm that urease is chemically adsorbed by the LDH surface. The aggregation of the LDH platelets can affect noticeably their adsorption capacity for enzymes and the preparation of LDH adsorbant appears to be a determinant step for the immobilization efficiency. [ZnRAl]-urease hybrid LDH was also prepared by coprecipitation with R = 2, 3 and 4 and Q= urease/ZnRAl from 1 /3 up to 2.5. For Q < 1.0,100 % of the urease is retained by the LDH matrix whatever the R value while for higher Q values an increase in the enzyme/LDH weight ratio leads to a decrease in the percentage of the immobilized amount.

PV A film/ Sodium tetraborate/ Proteolytic enzyme Protease C (Pr)+ polyhexamethyleneguanidine hydrochloride [PHMG], as antimicrobial (AM) -biological active material -increases the AM desorption rateby 1.5-4.5 times For PHMG with M, 10000, total desorption of AM from the film could be obtained 236... 

It can be seen from Eq. (5) that the maximum possible concentration on the surface, c, influences significantly the transport rate. This parameter is a function of the available surface area as well as of the density of the reactive sites. Because of that, the matrix structure plays a very important role in such adsorp-tion/desorption processes. In the case of biological reactions, where the chemical conversion is performed by immobilized enzymes, the immobilization also plays an important role in order to achieve an optimal enzyme density on the reactive surface. 

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