Abstract
The enzymatic hydrolysis of native cellulose has been discussed from the viewpoint of synergistic action of endo- and exo-type cellulases. However, the details in the mechanism remain unclear, partly because most studies have been generally employed to use certain types of cellulosic substrates being useful in measuring enzyme activity such as carboxymethylcellulose and Avicel instead of native cellulose with high resistance for the degradation because of its high crystallinity and water insolubility. The degree of crystallinity of cellulose is one of the most important structural parameters which affects the rate of enzymatic hydrolysis. Consequently, it is important to investigate the behavior of cellulase components in crystalline and amorphous regions of native cellulose. In the present review, we investigated the adsorption and hydrolysis modes of exo- and endo-type cellulases from Irpex lacteus for cellulose with different crystallinities, and confirmed that the crystallinity of substrate greatly affects the characteristic modes of attack of both cellulases. Moreover, the changes in the size of amorphous region of cotton cellulose with the progress of enzymatic cellulolysis were observed by differential scanning calorimetry in addition to the morphological investigation of the degradation process, and the mode of action of two types of cellulases in the amorphous and crystalline regions of native cellulose was clarified.
