MODES OF ACTION ON COTTON AND BACTERIAL CELLULOSE OF A HOMOLOGOUS ENDOGLUCANASE-EXOGLUCANASE PAIR FROM TRICHODERMA-REESEI

The endoglucanase I (EGI) and the cellobiohydrolase I (CBHI) of the fi lamentous fungus Trichoderma reesei form a homologous pair of cellulol ytic enzymes which nevertheless have different modes of action, We sho w here that the action of CBHI on bacterial microcrystalline cellulose results in efficient solubilisation but only a slow decrease in its d egree of polymerisation. In contrast, the action of EGI results in a r apid decrease of the degree of polymerisation but less efficient overa ll solubilisation of the substrate. CBHI alone was practically inactiv e toward cotton which has a high initial degree of polymerisation and a complex morphology. EGI rapidly reduced the degree of polymerisation of cotton, and slowly solubilised part of it Working synergistically, EGI and CBHI solubilised cotton more rapidly and to a greater extent than EGI alone. Our data are consistent with the exoglucanase nature o f CBHI and also provide some evidence supporting its processive mode o f action.