BINDING OF HEMICELLULASES ON ISOLATED POLYSACCHARIDE SUBSTRATES

Binding of five fungal xylanases produced by Trichoderma reesei, Asper gillus oryzae, and Aspergillus fumigatus and two mannanases of Bacillu s subtilis and T. reesei on insoluble xylan, mannan, and cellulose was studied at different pH values and ionic strengths. For comparison, t he binding of cellobiohydrolase I (CBH I) and endoglucanase (EG I) of T. reesei on the same substrates was examined. Ionic interactions appe ared to play an important role in the binding of xylan, as most of the enzymes were totally bound on xylan when the pH was below their isoel ectric point but remained mainly unbound at pH values above the isoele ctric point. The binding on xylan was also clearly sensitive to ionic strength. The xylanases were also incompletely bound on mannan and cel lulose, and the two mannanases tested were partially bound on mannan. The two cellulolytic enzymes of T. reesei used in this work are both k nown to contain a cellulose binding domain and were efficiently bound on cellulose. Interestingly, T. reesei mannanase was also found to bin d readily on cellulose. Thus, it most probably contains, instead of a mannan binding domain, a specific cellulose binding domain.