Conclusions
Basic and applied research carried out during the past decade has shown that cellulases and xylanases are of great intrinsic interest, and have a range of novel and valuable uses in biotechnology. Early biochemical studies of purified enzymes, coupled with more recent molecular studies utilizing recombinant DNA technologies, have provided detailed information on the biochemistry, architecture, Table 2.5. Applications of cellulases and xylanases. Extraction and clarification of fruit juices and...
CBHs cellobiohydrolases exoglucanases
Like endoglucanases, the CBHs are highly active on amorphous and swollen celluloses, but degrade crystalline cellulose and cello-oligosaccharides rather poorly Wood and Bhat, 1988 . These enzymes are specific for P-1,4 linkages of the cellulose chain, but are inactive on cellobiose, CM- and hydroxyethyl-celluloses. In general, CBHs attack cellulose chains from the non-reducing end and release cellobiose Wood et al., 1988 . Recent kinetic studies and high-resolution structural data confirmed...
Applications
In addition to their established use as animal feed additives, cellulases and xylanases have a wide range of applications in food, paper and pulp, textile, fuel and chemical industries Table 2.5 Mandels, 1985 Gilbert and Hazlewood, 1993 Beguin and Aubert, 1994 Bhat and Bhat, 1997 . In a wider context, these enzymes have potential uses in waste management, pollution treatment, protoplast production, genetic and protein engineering as well as other research and development programmes Table 2.5...
Fungal and bacterial endoxylanases
The mode of action of endoxylanases has been extensively studied Coughlan, 1992 Coughlan and Hazlewood, 1993a,b Biely et al., 1997 . In general, these enzymes cleave the internal P-1,4 linkages of the xylan backbone and release mainly xylobiose, xylotriose and substituted oligomers having two to four residues Table 2.2 . It has been reported that most endoxylanases cleave the xylan backbone leaving the substituent at the non-reducing end of the xylosyl chain or the oligosaccharide Dekker, 1985...
Quantitative assays for cellulases and xylanases
The cellulase system contains mainly endoglucanase EC 3.2.1.4, 1,4-P-D-glucan glucanohydrolase , exoglucanase or cellobiohydrolase EC 3.2.1.91, 1,4-P-D-glucan cellobiohydrolase and P-glucosidase or cellobiase EC 3.2.1.21, P-D-glucoside glucohydrolase . Endoglucanase activity is generally determined by measuring the reducing sugars released from either carboxymethyl CM- or hydroxyethyl HE- cellulose Wood and Bhat, 1988 . This activity can also be measured by determining either the decrease in...
Structure of Cellulose and Hemicellulose
Plant cell walls consist mainly of cellulose 40-45 , hemicellulose 30-35 and lignin 20-23 Ladisch et al., 1983 . Cellulose is alinear polymer of glucose linked by P-1,4-glycosidic bonds, having a simple primary and complex tertiary structures. The repeating unit of cellulose is cellobiose Fig. 2.1a . The degree of polymerization DP number of glucose residues per cellulose chain varies from 500 to 14,000 Marx-Figini and Schultz, 1966 . In plant cell walls, the cellulose chains are oriented in...