Abstract: The bifunctional enzyme(CCBE),which was purified from Trichoderma viride cellulase with cellulase-chitosanase activities,was modified by N-bromossuccinimide(NBS).The results indicated that NBS could both inactivate its cellulase activity and chitosanase activity.The kinetic analysis revealed that two tryptophan(Trp)residues were essential for its cellulase activity and one Trp residue for its chitosanase activity.93% protection by 0.5% chitosan against inactivation by NBS,compared with 60% protection by 0.5% CMC,showed that one Trp residue was at the CCBE substrate binding site for both of its cellulase activity and chitosanase activity,and one Trp residue was at the catalytic site of its cellulase activity.Km increase of NBS modified CCBE was detected.These information confirmed above.

Key words: bifuctional enzyme, tryptophan residues, chemical modification