Fine Substrate Specificities of Four Exo-Type Cellulases Produced by Aspergillus niger, Trichoderma reesei, and Irpex lacteus on

To investigate the fine substrate specificities of four highly purified exo-type cellulases (Exo-A from Aspergillus niger, CBHI and CBH11 from Trichoderma reesei, and Ex-1 from Irpex lacteus), water-soluble substrates such as barley glucan, xyloglucan from tamarind (Tamarindus indica L.), and their oligosaccharides were employed. Four exo-type cellu-lases immediately hydrolyzed 3-0-;9-D-cellotriosylglucose to produce cellobiose and laminaribiose. In contrast, CBEQI showed no hydrolytic activity towards 32-0-y9-D-cello-biosylcellobiose, which was hydrolyzed to cellobiose by the other exo-type cellulases. These cellulases hydrolyzed the internal linkages of barley glucan and lichenan in an endo-type fashion to produce cellobiose and mix-linked oligosaccharides as main products. The DP-lowering activities of the four exo-type cellulases on barley glucan were in the order of Ex-1, CBHII, Exo-A, and CBHI. Based on gel permeation chromatography analysis of the hydrolysates, Ex-1 seemed to attack the internal cellobiosyl unit adjacent to J3-1,3-glucosidic linkages in barley glucan molecule more frequently than did the other cellulases. Xyloglucan was hydrolyzed only by CBHI and CBHII, and produced hepta-, octa-, and nona-saccharides. In addition, a xyloglucan tetradecasaccharide (XG14) wa