Between xylandegrading enzymes

Efficient and complete hydrolysis of xylan requires the synergistic action of main-and side-chain-cleaving enzymes with different specificities (Coughlan et al., 1993 Coughlan and Hazlewood, 1993a). For xylan-degrading enzymes, it is difficult to demonstrate the synergism by measuring only the reducing sugars produced, because of the heterogeneous nature of the substrate. Hence, the hydrolysis products must be separated, identified and quantified in order to obtain a detailed picture of the...

Other Characteristics of Cellulases and Xylanases Induction and regulation

Induction and regulation of microbial cellulases and xylanases have been the subject of detailed investigation (Ryu and Mandels, 1980 Kubicek, 1992 Biely, 1993 Kubicek et al., 1993 Saloheimo et al., 1998). Both cellulases and xylanases are inducible enzymes. It has been reported that cellulose or cellulose-rich material and xylan or xylan-rich material are the best carbon sources for the production of high levels of cellulases and xylanases by many microorganisms (Ryu and Mandels, 1980 Biely,...

Multiplicity of cellulases and xylanases

Most microorganisms capable of degrading cellulose and xylan produce multiple forms of cellulases and xylanases with either very similar substrate specificities or varying substrate specificities (Wong etal., 1988 Bhat etal., 1989). Based on biochemical studies, it has been reported that T. reesei and P. pinophilum produce two forms of CBHs and four to seven forms of endoglucanases (Gong etal., 1979 Wood et al., 1988 Bhat and Wood, 1989), whereas A. niger, T. viride and T. emersonii produce 15,...

Enzymology of Cellulases and Xylanases Source

Cellulases and xylanases are produced by a wide range of bacteria and fungi, including aerobes, anaerobes, mesophiles, thermophiles and extremophiles. Aerobic fungi and bacteria generally produce extracellular cellulases and hemicellulases. Interestingly, anaerobic bacteria Clostridium thermocellum, C. cellulovorans, Ruminococcus albus, R. flavefaciens, Fibrobacter succinogenes, Acetivibrio cellulolyticus and anaerobic fungi Neocallimastixfrontalis, N. patriciarum, Piromyces equi produce...

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...

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

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...