PINE SUBSTRATE SPECIFICITIES OF 4 EXO-TYPE CELLULASES PRODUCED BY ASPERGILLUS-NIGER, TRICHODERMA-REESEI, AND IRPEX-LACTEUS ON (1-]3),(1-]4)-BETA-D-GLUCANS AND XYLOGLUCAN

To investigate the fine substrate specificities of four highly purifie d exo-type cellulases (Exo-A from Aspergillus niger, CBHI and CBHII fr om Trichoderma reesei, and Ex-1 from Irpex lacteus), water-soluble sub strates such as barley glucan, xyloglucan from tamarind (Tamarindus in dica L.), and their oligosaccharides were employed, Four exo-type cell ulases immediately hydrolyzed 3-O-beta-D-cellotriosylglucose to produc e cellobiose and laminaribiose. In contrast, CBHII showed no hydrolyti c activity towards 3(2)-O-beta-D-cellobiosylcellobiose, which was hydr olyzed to cellobiose by the other exo-type cellulases. These cellulase s hydrolyzed the internal linkages of barley glucan and lichenan in an endo-type fashion to produce cellobiose and mix-linked oligosaccharid es as main products, The DP-lowering activities of the four exo-type c ellulases on barley glucan were in the order of Ex-1, CBHII, Exo-A, an d CBHI. Based on gel permeation chromatography analysis of the hydroly sates, Ex-1 seemed to attack the internal cellobiosyl unit adjacent to beta-1,3-glucosidic linkages in barley glucan molecule more frequentl y than did the other cellulases. Xyloglucan was hydrolyzed only by CBH I and CBHII, and produced hepta-, octa-, and nona-saccharides. In addi tion, a xyloglucan tetradecasaccharide (XG14) was split only to heptas accharide (XG7) by CBHI and CBHII.