A novel chitinase having a unique mode of action from Aspergillus fumigatus YJ-407

Chitinases are produced throughout the growth process of fungi and are thou ght to play important roles in morphogenesis. Aspergillus fumigatus, is an important pathogen of immunocompromised individuals in which it causes pneu monia and invasive disseminated disease with high mortality; it is also kno wn to produce chitinase. We have induced an exceptionally stable extracellu lar chitinase in A. fumigatus YJ-407, which could be isolated readily in a homogeneous form by using ammonium sulfate precipitation followed by DEAE-c ellulose chromatography and preparative PAGE. The molecular mass of this ch itinase was estimated to be 46 000 by SDS/PAGE, and its isoelectric point w as pH 5.6. The enzyme was most active at pH 5.0 and 60 degreesC, and was in hibited strongly by Hg2+, Pb2+, Ag+, Fe2+, Mn2+ and Zn2+. The enzyme was st able over a broad pH range 4-8 and below 45 degreesC. Tryptophan and carbox yl groups were found to be essential for the enzyme activity. The Michaelis constants for swollen chitin and chitosan were 1.12 mg.mL(-1) and 1.84 mg. mL(-1), respectively. The enzyme showed maximum activity towards glycol chi tin and partially deacetylated chitosan, and lower activity towards colloid al chitin. Analysis of the hydrolysis product showed that the enzyme has bo th endo- and exo-hydrolytic activities. In addition, a transglycosyl activi ty was also observed.