Hemicellulolytic enzymes

In the treatment of cellulose pulps one essential criterion for a suitable enzyme preparation is that its cellulase activity should be as low as possible, or preferably absent completely. As even extremely low cellulase activities may ruin pulp quality, Trichoderma enzyme preparations are unlikely to be suitable for these applications. Many bacterial and fungal enzymes with low cellulase activity have been shown to be suitable for treatment of pulps 14, 15, 16,17), Regulation of the often synchronous production of cellulolytic and hemicellulolytic enzymes in micro-organisms is not well understood, and is further complicated by substrate cross-specificity of these enzymes. Enzymes with both endoglucanase and xylanase activity have been reported for bacteria 18, 19) and fungi 20, 21, 22), In addition to selection of strain and... 

The culture filtrates of T. reesei contained a large number of both cellulolytic and hemicellulolytic enzymes, which could be partially separated by chromatofocussing (Fig. 1). Of the cellulolytic enzymes, several endoglu-canases and two cellobiohydrolases have already been isolated and characterized (30). Some of the endoglucanases isolated are nonspecific and have xylanase activity (31). The two major xylanase (Xyl) peaks in Figure 1 corresponded to pi-values of above 7.5 and 5.5. When the former enzyme was further purified (24), its isoelectric point was found to be about pi 9 (Table I). Previously, the presence of at least three electrophoretically different xylanases in T. reesei culture filtrates was reported, with the most acidic one shown to have broad substrate specificity (10). This is in agreement with the reported occurrence of three xylanases (pi > 7, pi 5.1, pi... 

Index Entries Cellulolytic enzymes hemicellulolytic enzymes enzymatic hydrolysis coinduction. 

In the present study, the fermentation of glucose and xylose model solutions and hydrolysate samples from steam-pretreated aspen was investigated. After the steam explosion, the obtained slurry was suspended in water to a solid-to-liquid ratio of 200 g/L of dry matter (DM) and enzymatically hydrolyzed with a mixture of cellulolytic and hemicellulolytic enzymes. Subsequently, the hydrolysate was detoxified using a two-step treatment through cationic and anionic resins. 

Wheat SFF material was kindly donated by Amylum UK (Nesle, France). The material had a dry matter (DM) content of 18.5% and was stored in buckets at -18°C. The composition, analyzed by combined acid hydrolysis with 1% H2S04 followed by enzymatic hydrolysis with cellulolytic and hemicellulolytic enzymes, is given in Table 1. 

Table 1 Specific activities (mean of triplicate determinations standard deviation) of cellulolytic and hemicellulolytic enzymes of selected preparations. 

S. rolfsii is known to produce cellulolytic and hemicellulolytic enzymes in high amounts (1-3), as a matter of fact it has been recognized as one of the few producers of these hydrolases that are of industrial interest (4). S. rolfsii secretes a complete cellulose degrading enzyme system consisting of endoglucanases (5, 6), cellobiohydrolases (7), and (3-D-glucosidases (8) which have been isolated and characterized extensively in the past. In addition, cellobiose dehydrogenase was reported as part of the cellulolytic enzyme system of S, rolfsii (9, 10). 

Rakotoarivonina H, Herman B, Monthe N, Remond C. (2012). The hemicellulolytic enzyme arsenal of Thermobacillus xylanolyticus depends on the composition of biomass used for growth. Microb Cell Fact, 11, 159. 

Sakamoto T, Hasunuma T, Hori Y, Yamada R, Kondo A. (2011). Direct ethanol production from hemicellulosic materials of rice straw by use of an engineered yeast strain codisplaying three types of hemicellulolytic enzymes on the surface of xylose-utilizing Sacchammyces cerevisiae cells. J Biotechnol, 158, 203-210. 

FIGURE 8 A recombinant yeast strain displaying hemicellulolytic enzymes such as xylanase and p-xylosidase on the cell surface and expressing xylose-assimilating enzymes such as XR, XDH, and XK. 

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