Long Term Stability

The stabilities of enzymes in solution and immobilized on the cotton fibers were estimated by following their respective activities with time. Figure 10A,B shows a decrease in activity over time in both cases. However, the activities of immobilized enzymes on cotton fibers remained higher

Fig. 10. Stability of pepsin (A) and trypsin (B) in solution and immobilized on cotton fibers

than that in solution (about 1.66 times higher in the case of pepsin and 2.4 in the case of trypsin). A life-time of over 1 month for the enzyme-modified cotton biocatalytic material, corresponding to a loss of only the half of the initial activity, was observed, which represents to some extent an appreciable stabilization of the enzyme reactivity by the immobilization process.

In conclusion, the feasibility and the efficiency of the elaboration of an enzymatic membrane made ofproteases immobilized onto cotton fibers by tosyl activation is demonstrated. Cotton was activated with tosyl chloride and used as a novel fibrous matrix for biocatalyst immobilization. The described procedure is simple, inexpensive, and industrially applicable; moreover, it provides highly active and stable immobilized biocatalyst support. The very simple method for immobilization using tosyl-activated cotton and the appreciable working lifetime (over 1 month) of the cotton-immobilized enzyme reactor should have many applications in industrial biocatalysis (e.g., peptide production with pepsin and synthesis of insulin with trypsin).

Immobilization of Uricase and Xanthine Oxidase on Ion-Exchanging Textiles

Ion-exchanging textiles have been used as organic supports for enzyme immobilization with the aim of developing reactive woven materials that can be substituted into membrane systems in bioreactors or that can act, for instance, as reactive bags for waste treatment devices, thus extending the range of their potential applications. The cationic or anionic sites of ion-exchanging textiles are used for enzyme immobilization by classical chemical routes (chemical bonding) and by a biomimetic molecular recognition attachment process (complexation between biotin and avidin). As a result of the comparison between both processes used for enzyme immobilization, it has been shown that the biomimetic latter route is much more efficient than the classical routes, improving both the enzyme specific activity and their lifetime.

The chemical structure of the matrix of the ion-selective membranes used in electromembrane processes (for instance electrodialysis) is not very different from that of ion-exchanging textiles. These membranes can be associated with textiles in coupled processes like electrodeionization (Dejean et al. 1997) or, better still, can be substituted into membranes for applications such as chemical conversion.

The association of textile and enzyme is already used in the textile industry. Enzymes can be used in diverse textile areas ranging from fabric prepa ration to fabric destruction. Enzymes may be used at each wet-processing step, for example lipase or amylase for resizing, pectinase or cellulase for scouring (Buschle-Diller et al. 1998), and oxidoreductase for bleaching, dying, and finishing (Nolan Etters 1998). Immobilization of an enzyme on the textile can be utilized in the development new functionalized textiles for use not only in the clothing industry, but also as a catalytic material. Moreover, the porosity of a textile with associated enzyme catalytic activity can allow to the production of a kind of chemically reactive enzyme filtration membrane.

We present here few examples of a system comprising an ion-exchanging tissue, in the core of which enzymes acting as catalysts have been grafted either by a chemical route or by a biomimetic molecular recognition process (complex formation).

Comparison between the activity of tissues immobilizing enzymes by covalent bonding and that immobilizing enzymes by molecular recognition reveals that the latter biomimetic immobilization process is more effective, presumably because of the mildness of this process, which preserves the specific activity of the immobilized enzyme.

Textile supports are made of nonwoven cellulose fibers that are modified by ion-exchange groups (carboxylic, tertiary amine, or ammonium). The grafting ratio is 20%, with an average polymerization degree of 50-200, the specific mass and the cut-off being 450 g/m2 and 0.1 mm, respectively (Institut Textile de France 1987).

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