Hydrolytic enzymes, cellulose

Two broad areas of application for xylanolytic enzymes have been identified (1). The first involves the use of xylanases with other hydrolytic enzymes in the bioconversion of wastes such as those from the forest and agricultural industries, and in the clarification and liquification of juices, vegetables and fruits. For these purposes, the enzyme preparations need only to be filtered and concentrated as essentially no further purification is required. Several specific examples of applications involving crude xylanase preparations include bioconversion of cellulosic materials for subsequent fermentation (2) hydrolysis of pulp waste liquors and wood extractives to monomeric sugars for subsequent production of single cell protein (3-5). Xylose produced by the action of xylanases can be used for subsequent production of higher value compounds such as ethanol (6), xylulose (7) and xyIonic acid (8-9). 

A few animals (especially ruminants and termites) are able to metabolize cellulose, but even these animals depend on appropriate microorganisms in their intestinal tracts to hydrolyze the -1,4 links other animals, including man, cannot utilize cellulose as food because they lack the necessary hydrolytic enzymes. However, such enzymes are distributed widely in nature. In fact, deterioration of cellulose materials —textiles, paper, and wood —by enzymatic degradation (such as by dry rot) is an economic problem that is not yet adequately solved. Efforts to turn this to advantage through enzymatic hydrolysis of cellulose to glucose for practical food production have not been very successful (see Section 25-12). 

Figure 1. Cooperative action of enzymes of the cellulase system in hydrolytically converting cellulose to glucose...

Since essentially all of the protein in the cellulose-grown culture or the sophorose-incubation mixture can be accounted for by the three principal proteins and the / -glucosidase, it seems reasonable to conclude that the multiplicity of enzymes seen after several days of culture growth are caused by degradation. This may be attributable either to inherent instability (3) or to the presence of hydrolytic enzymes (16). There seems to be no evidence for the Ci enzyme as a nonhydrolytic or affinity factor, since all known enzymes of the system are hydrolytic. That the sophorose-stimulated system (with no possible loss of the Ci ... 

Both the quantity and properties of cellulases produced by microorganisms depend on the culture conditions. Commonly, cellulases are produced by culture of the organism either (a) in a liquid medium, which may be stationary, shaken, or submerged with aeration, or (b) by a Koji process on a solid substrate such as wheat bran (7). The complexity of the crude cellulosic carbon source usually leads to the production of a mixture of hydrolytic enzymes which may include amylases, proteases, chitinases, etc., in addition to the cellulases. Separation of proteins from culture filtrates by high resolution techniques such as chromatography, electrophoresis, or electrofocusing often reveals a number of enzyme species which may differ in specificity toward cellulosic substrates. These forms may represent ... 

Figure 6. Both hydrolytic and oxidative enzymes participate in cellulose decomposition by the white-rot fungus Phanerochaete chrysosporium Burds. Hydrolytic enzymes i, endo-1 - - I ucanases 2, exo-1,4- -glucanase and 3, -glucosidase. Oxidative enzymes 4, glucose oxidase, 5, cMlobiose oxidise and 6, cellobiose quinone oxidoreductase. Adapted from Reference 23,...

In the study of herbicide metabolism, it has been observed that the parent compound and its metabolites can be incorporated into lignin, cellulose, and some proteins. These products are insoluble, resistant to hydrolytic enzymes, immobile, and consequently nontoxic. Rigorous procedures may be needed to release the metabolite for analysis. ... 

The enzyme mechanisms involved in degradation of cellulose by the white-rot fungus Sporotrichum pulverulentum have been reviewed.The hydrolytic enzymes involved include (i) five 4)-i3-D-glucanases, (ii) one exo-... 

Biodegradation reactions are typically enzyme catalyzed and occur in aqueous media. Natural macromolecules containing hydrolyzable linkages, such as protein, cellulose and starch, are generally susceptible to biodegradation by the hydrolytic enzymes of microorganisms. 

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