ACTION OF EXO-TYPE AND ENDO-TYPE CELLULASES FROM IRPEX-LACTEUS ON VALONIA CELLULOSE

Cellulolytic mode of action of the two highly purified exo- and endo-t ype cellulases from Irpex lacteus on pure Valonia cellulose was invest igated. Electron microscopy substantiated that both cellulases are ads orbed preferentially into the internal parts of microfibrils in the ne twork structure of the cellulose at initial stages before enzymatic hy drolysis, and that the adsorption ratio of both cellulases onto the ex ternal surfaces of microfibrils increased with incubation time althoug h this tendency was less remarkable with the exo-type cellulase than w ith the endo-type one. The exo-type cellulase exhibited relatively hig h activity producing cellobiose throughout 12-h incubation, while the endo-type cellulase produced small amounts of cellooligosaccharides. T he degree of polymerization was far more suppressed by the endo-type c ellulase than by the exo-type one. Degradation by the cellulases in ty pical exo- and endo-fashions yielded quite different morphological pat terns in the microfibrils. Exo-type cellulase loosened the network str ucture of microfibrils and made them slightly thinner, while endo-type cellulase caused conspicuous swelling and dissolution of individual m icrofibrils.