HYDROLYSIS OF COTTON CELLULOSE BY EXO-TYPE AND ENDO-TYPE CELLULASES FROM IRPEX LACTEUS - DIFFERENTIAL SCANNING CALORIMETRIC STUDY

The mode of hydrolysis of cotton cellulose by two highly purified exo- and endo-type cellulases from Irpex lacteus was investigated by diffe rential scanning calorimetry, to measure changes in the size of the am orphous region in cotton fibers with the enzymatic reaction. The cellu lases induced entirely different changes in the size of the amorphous region, particularly at earlier stages of reaction. Exo-type cellulase gradually reduced the amorphous region with release of cellobiose fro m the initial stage of hydrolysis, but began to increase the amorphous region at more advanced stages of hydrolysis. By contrast, endo-type cellulase caused no liberation of reducing sugar at the initial stage of hydrolysis but caused a sharp increase in the amorphous region, and it thereafter caused a rapid decrease of the amorphous region, accomp anied with the production of various kinds of cellooligosaccharides. T he rate of size reduction of the amorphous region caused by endo-type cellulase was much higher than that by exo-type cellulase. Convergence of the decrease in the size of amorphous region during hydrolysis by endo-type cellulase is followed by the increase in this region being i nfluenced by further hydrolysis of remained crystalline region. Substa ntial changes in the morphology of cotton occurred with the two cellul ases after the hydrolysis stages at which the size of the amorphous re gion was minimum.