Abstract
In cellulolytic organisms, there are at least three cellulase components which together constitute a multienzyme system, and cellulosic substrates are converted to soluble sugars by their synergistic action. These components are an exo-cellulase, an endo-cellulase and a βglucosidase. However, the modes of degradation of cellulose have not been fully established. The modes of hydrolysis of highly purified cellulases, exo- and endo-cellulases, from fungi (Irpex lacteus, Trichoderma reesei, and Aspergillus niger) were investigated by using pure cellulosic materials with different crystallinities (CrI) and modified cellulose as substrates . In productivity of reducing sugar, exo-cellulases hydrolyzed effectively celluloses as compared with endo-type cellulases, and saccharifying activities of both cellulases, especially of endo-cellulases, drastically increased in parallel with decreasing CrI. Endo-cellulases lowered the degree of polymerization (DP) of crystalline celluloses much intensively as compared with exo-type cellulases, and DP lowering activity of endo-cellulase decreased with decreasing CrI. In the hydrolysis products, endo-cellulases produced several oligosaccharides from H3PO4-treated celluloses, but not from native celluloses, while exo-cellulases produced only cellobiose from insoluble celluloses. It was found that each cellulase component showed clearly the action of exo- and endo-fashion on the hydrolysis of insoluble cellulose, especially native cellulose as substrate . However, the strictness of their fashion was not obscure on the modified substrate such as p-nitrophenylβ-glycosides. Electron microscopy photographs showed clearly different morphologic changes of substrates treated with exo- and endo-cellulases. In the hydrolysis by exo-cellulase, the transverse deep cracks were observed on the surface of native cellulose and these cracks extended from fiber surface to lumen structure located in the inside of fiber . In endo-cellulase, these cracks seemed to be shallow and erosion areas were observed on the outside surface of fiber and lumen region. On the basis of these observations, it may be concluded that the hydrolysis by exo- and endocellulases produces quite different morphologic patterns with native cellulose, but little differences with H3PO4-treated celluloses. Basing on the results from these fungi, it may be concluded that the mode of action of exoand endo-cellulase is dependent on the structure of cellulose used as substrate .
