Cellulase properties

In one study [90], enzyme pretreatment increased colour yield without affecting fastness properties. However, pretreatment of cellulosic fibres with cellulase lowered the subsequent fixation of homobifunctional triazine reactive dyes but did not impair the fixation of other types of reactive dyes [91]. Another study suggested that the enhanced brightness of reactive dyeings was greater with triazine dyes than with vinylsulphone types when cotton was pretreated or aftertreated with cellulase [92]. 

Our early studies dealt with characterization of cellulase from Clostridium thermocellum (4, 5), the first described thermoanaerobe. More recently, we have characterized the saccharidases in three new non-cellulolytic thermoanaerobic species (6-12). Table II compares the general properties of thermophilic saccharidases identified in C. thermosulfurogenes strain 4B (6), C. thermohydrosulfuricum strain 39E (7), and Thermoanaerohacter strain B6A (13). It is worth noting here that... 

For Trichoderma reesei the cellulases most thoroughly investigated with respect to their structural properties are CBH I and CBH II and to a lesser extent the two en-doglucanases (EG I and EG III) 11 (Table I). For most other cellulases structural characterizations are confined to the amino add sequence as deduced from the base sequence of the respective genes and to sequence related investigations such as hydro-phobic cluster analysis 10 or computer aided molecular modelling and homology... 

These results demonstrate several useful properties of the C. fimi CBDs for enzyme immobilization and purification. Presumably, the CBDs of other bacterial cellulases (Figure 3) can be used in similar ways. It remains to be seen whether these differ significantly in their affinity or capacity for adsorption if so, certain CBDs may be preferable for specific purposes. 

Another method which may become a useful technique for selective inactivation of cellulases in enzyme mixtures is the use of selective heat inactivation. While establishing the thermostability properties of crude xylanases from a fungal strain Y-94, Mitsuishi et al. (80) observed differential heat labilities of the cellulase and xylanase activities in the culture filtrate. After an incubation period of 20 minutes at 65°C, the xylanase activity was reduced by 5-10% whereas the Avicelase and /3-glucosidase activities were reduced by 100% and 60%, respectively. We have observed a similar temperature dependency of xylanase and cellulase activities in T. auranti-acus. As indicated in Figure 2, treatment of the culture filtrate at 70°C for 20 minutes resulted in less than a 5% loss in xylanase activity whereas cellulase activities were reduced by 40-50%. A similar effect has also been observed for the xylanases and cellulase enzymes produced in culture filtrates from T. harzianum (93). Further work in the area of heat treatments may improve the effectiveness of cellulase inactivation. Since the cellulase activities of some enzyme preparations can be more rapidly inactivated on... 

An important chemical finishing process for cotton fabrics is that of mercerization, which improves strength, luster, and dye receptivity. Mercerization involves brief exposure of the fabric under tension to concentrated (20—25 wt %) NaOH solution (14). In this treatment, the cotton fibers become more circular in cross-section and smoother in surface appearance, which increases their luster. At the molecular level, mercerization causes a decrease in the degree of crystallinity and a transformation of the cellulose crystal form. These fine structural changes increase the moisture and dye absorption properties of the fiber. Biopolishing is a relatively new treatment of cotton fabrics, involving cellulase enzymes, to produce special surface effects (15). 

Tuerker and Mavituna immobilized Trichoderma reesei within the open porous networks of reticulated polyurethane foam matrices. Growth pattern, glucose consumption, and cellulase production were compared with those of freely suspended cells. The method of immobilization was simple and had no detrimental effect on cell activity. Hundreds of similar projects could be cited. Not all rated the use of polymethane as the preferred technique. If a statistical analysis were conducted on aU the immobilization literature, we are sure that no single technique would be dominant. However, the combination of ease of immobilization, cost of materials, flow-through properties, control of flux rate through the immobilizing membrane, high surface-to-volume ratio, and other factors make polymethane a viable substratum for the continuous production of proteins. 

Wool-Cellulasic Fibers. One of (he oldest fiber blends in (he textile market is (he combination of wool and cotton or wool and viscose. In a one-bath process, selected direct and acid dyes are applied at pH 4.5-5.0 at 98 ItXfC. A phenolsulfonie acid condensation prodact is added as a reserving agent, to prevent the direct dyes from dyeing the wool under acid conditions, if optimum wetfastness properties are required, fiber-reactive dyes can be applied to both fibers by use of a two-bath process. 

The Mode of Enzymatic Degradation of Cellulose Based on the Properties of Cellulase Components... 

With this background, we then tried to obtain the possible exocellulase component from I. lacteus using Driselase as the starting material, and we succeeded in isolating it. Its enzymatic properties were also precisely investigated and the possible role of this cellulase component in vivo was discussed with reference to the properties of other cellulase components already published. This report deals with these results, but most of the data for F-l and S-l were cited from previous work (2,3). 

Two Pea Cellulases Display the Same Catalytic Mechanism Despite Major Differences in Physical Properties... 

Physical Properties. All of the cellulase (CMCase) activity which develops in auxin-treated pea apices dissolves in salt solutions (e.g., phosphate buffer, 20mM, pH 6.2, containing 1M NaCl). Gel chromatography of such extracts indicates the presence of two cellulase components with similar levels of activity and elution volumes corresponding to molecular weights of about 20,000 and 70,000 (Figure 1). If the tissue is extracted with buffer alone, only the smaller cellulase dissolves (referred to as buffer-soluble or BS cellulase). The larger buffer-insoluble (BI) cellulase can then be extracted from the residue by salt solutions. This simple extraction procedure effectively separates the two cellulases, and can be used as an initial step for their estimation or purification. 

Oxidation of two out of 13 tryptophan residues in a cellulase from Penicillium notatum resulted in a complete loss of enzymic activity (59). There was an interaction between cellobiose and tryptophan residues in the enzyme. Participation of histidine residues is also suspected in the catalytic mechanism since diazonium-l-H-tetrazole inactivated the enzyme. A xylanase from Trametes hirsuta was inactivated by N-bromosuc-cinimide and partially inactivated by N-acetylimidazole (60), indicating the possible involvement of tryptophan and tyrosine residues in the active site. As with many chemical modification experiments, it is not possible to state definitively that certain residues are involved in the active site since inactivation might be caused by conformational changes in the enzyme molecule produced by the change in properties of residues distant from the active site. However, from a summary of the available evidence it appears that, for many / -(l- 4) glycoside hydrolases, acidic and aromatic amino acid residues are involved in the catalytic site, probably at the active and binding sites, respectively. 

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