Isolation and characterization of thermostable chitinases from Bacillus licheniformis X-7u.

Four kinds of thermostable chitinase were isolated from the cell-free culture broth of Bacillus licheniformis X-7u by successive column chromatographies on Butyl-Toyopearl, Q-Sepharose, and Sephacryl S-200. We named the enzymes chitinases I(89 kDa), II(76 kDa), III(66 kDa) and IV(59 kDa). Chitinases II, III and IV possessed extremely high optimum temperatures (70-80 degrees C), showing remarkable heat stability. Chitinases II, III and IV produced (GlcNAc)2 and GlcNAc from colloidal chitin and chitinase I predominantly produced (GlcNAc)2. The action pattern of chitinase I on PN-(GlcNAc)4 also showed a stronger propensity to cleave off the (GlcNAc)2 unit from the non-reducing end than the other three chitinases. Chitinases II, III and IV catalyzed a transglycosylation reaction that converted (GlcNAc)4 into (GlcNAc)6.