Abstract
Two cellobiohydrolases belonging to the glycoside hydrolase family 7, FvCel7A and FvCel7B, were purified from the extracellular fluid of the cellulose-degrading culture of Flammulina velutipes. Hydrolytic activities and binding properties of these enzymes were investigated. Kinetic parameter (kcat/ Km-value) of FvCel7A for the hydrolysis of p-nitrophenyl-β-D-lactoside was 0.069s-1・mM-1, whereas that of FvCel7B was 0.15s-1・mM-1, which is two-fold higher than that of FvCel7A. However, the hydrolytic activity of FvCel7A for amorphous cellulose was higher than that of FvCel7B, suggesting better affinity of FvCel7A to insoluble substrate. Both enzymes could not hydrolyze crystalline cellulose prepared from Cladophora sp., although FvCel7A carries a cellulose-binding domain (CBD) belonging to the carbohydrate binding module family 1. Surprisingly FvCel7A was adsorbed on crystalline chitin effectively but not on crystalline cellulose. This causes unavailability of crystalline cellulose for FvCel7A as substrate regardless of its possession of family 1 CBD.
