Deactivation of cellulases

In the case of pH strategies III and IV, no remarkable differences in the growth and production rate of cellulases were seen up to h 52 of fermentation (data not shown), after which deactivation of cellulases was detected. 

Gunjikar, T. P., Sawant, S. B., and Joshi, J. B. 2001. Shear Deactivation of Cellulase, Exoglucanase, Endoglucanase, and P-Glucosidase in a Mechanically Agitated Reactor. Biotechnol. Prog., 17,1166-1168. 

Deactivation of cellulases after the desired effects have been achieved is very important. If the enzyme is not completely removed from the fabric, or is not effectively deactivated, the hydrolysis reaction will continue, although at a slower rate. As very large molecules, cellulases cannot diffuse into the crystalline parts of the cellulose fibres. They react on the fibre surface, so fibre damage takes time. But eventually enough hydrolysis will have taken place to weaken the affected fabrics or garments, leading to customer complaints and returns. 

Azevedo, H., Bishop, D., and Cavaco-Paulo, A. 2002a. Possibilities for Recycling Cellulases After Use in Cotton Processing. Part I Effects of End-Product Inhibition, Thermal and Mechanical Deactivation, and Cellulase Depletion by Adsorption. Appl. Biochem. Biotechnol., 101, 61-75. 

Not all cellulase enzymes give identical results, even with similar fabrics in similar equipment. Cellulases derived from Trichoderma typically are the most aggressive in their action, whereas mono-component endo-glucanases often require the most mechanical action to achieve the desired effects. Slow deactivation of the cellulases during transport and storage can adversely affect the reproducibility of the resulting effects. If cotton is not washed carefully before bio-finishing,... 

Another interesting strategy to combine an enzyme and an ionic liquid in a biocomposite configuration was reported by Vaultier et al [128]. Cellulase was immobilized onto a polymeric support (Amberhte XAD4) coated with a hydrophobic ionic liquid ([N jJ [NTfJ) and tested in saccharification of IL-dissolved cellulose. The presence of amberhte as a cover avoided the deactivation of the cellulose in the hydrophiHc medium [128]. 

However, Thomas and Dimnill (1979) studied the effect of shear on catalase and urease activities by using a coaxial cylindrical viscometer that was sealed to prevent any air-liquid contact. They found that there was no significant loss of enzyme activity due to shear force alone at shear rates up to 106 sec-1. They reasoned that the deactivation observed by Charm and Wong (1970) was the result of a combination of shear, air-liquid interface, and some other effects which are not fully understood. Charm and Wong did not seal their shear apparatus. This was further confirmed, as cellulase deactivation due to the interfacial effect combined with the shear effect was found to be far more severe and extensive than that due to the shear effect alone (Jones and Lee, 1988). 

Undesirable deactivation may be caused by high temperature and time, for example, caused by transport and storage and also by enzyme poisons such as certain surfactants (especially cationic ones), formaldehyde-containing products or heavy metal ions. An activation effect on cellulases was reported by Nicolai and co-workers. Alkaline pretreatment, low concentrations of selected non-ionic surfactants, polycarboxylic acids and polyvinyl pyrrolidone can enhance the bio-fmishing of cellulosics. 

Kim et al. [41] reported that a significant deactivation was observed when cellulase was subjected to shear and/or exposed to air-liquid interface, which was thought to be far more severe and extensive than shear effect alone. By using sufficient additives (surfactants and non-catalytic proteins, e.g., BSA), cellulase deactivation can be, to some extent, prevented, and cellulase can be stabilized. This might be because the addition of non-ionic surfactants could reduce the contact of enzymes with the air-liquid interface because of the surface... 

Biopolishing removes the protruding fibers of a fabric through the action of an enzyme. Enzymes, such as cellulase for cotton, selectively remove protruding fibers. These enzymes may be deactivated by an increase in temperature. 

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