SYNERGISTIC ACTIONS OF EXO-TYPE CELLULASES IN THE HYDROLYSIS OF CELLULOSE WITH DIFFERENT CRYSTALLINITIES

The synergistic actions of pairs of seven different exo- and endo-type cellulases produced by Irpex lacteus (Ex-1 and En-1), Trichoderma ree sei (CBH I, CBH II, and Endo-2), and Aspergillus niger (Exo-A and EG-1 ) were investigated using pure cellulosic materials with different cry stallinities as substrates. A marked synergism was observed with certa in combinations of exo-type cellulases, namely, CBH II and the other e xo-type cellulases (Ex-1, CBH I, or Exo-A), when saccharification acti vity against crystalline and amorphous celluloses was investigated. Di fferences between the modes of action of each exo-type cellulase alone and in combination are not clearly observed; the production of cellob iose was accelerated during the hydrolysis of crystalline and amorphou s celluloses by the combinations of exo-type cellulases, and no effect ive synergistic actions of the combinations of exo-type cellulases wer e noted in the depolymerization of crystalline cellulose. However, the synergistic actions of exo-type cellulases with CBH II caused specifi c changes in the surface features of highly crystalline celluloses. Ch aracteristic morphological changes in cotton fibers (erosion and crack ing of fiber surfaces) were induced at increasing rates by the combina tion of CBH II and Ex-1 or Exe-A. In contrast, destruction and subdivi sion of fibrils, which resulted in the pronounced fibrillation of cott on fibers, were observed after the treatment of cotton fibers with CBH II and CBH I. It was suggested that CBH II may be one of the key enzy mes involved in the synergistic actions during cellulose hydrolysis.