Purification and enzymatic properties of the extracellular and constitutive chitosanase produced by Bacillus subtilis RKY3

摘要

BACKGROUND: Purification and enzymatic properties of a chitosanase from Bacillus subtilis RKY3 have been investigated to produce a chitooligosaccharide. The enzyme reported was extracellular and constitutive, which was purified by two sequential steps including ammonium sulfate precipitation and ion exchange chromatography. RESULTS: Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified chitosanase revealed one single band corresponding to a molecular weight of around 24 kDa. The highest chitosanase activity was found to be at pH 6.0 and at 60 °C. Although the mercaptide forming agents such as Hg~(2+) (10 mmol L~(-1)) and p-hydroxymercuribenzoic acid (1 mmol L~(-1), 10 mmol L~(-1)) significantly or totally inhibited the enzyme activity, its activity was enhanced by the presence of 10 mmol L-1 Mn~(2+). The enzyme showed activity for hydrolysis of soluble chitosan and glycol chitosan, but colloidal chitin, carboxymethyl cellulose, crystalline cellulose, and soluble starch were not hydrolyzed. The analysis of chitosan hydrolysis by thin-layer chromatography and viscosity variation revealed that the purified enzyme should be endosplitting-type chitosanase. CONCLUSION: The chitosanase produced by Bacillus subtilis RKY3 was a novel chitosanlytic enzyme with relatively low molecular weight, which is a versatile enzyme for chitosan hydrolysis because it could hydrolyze soluble chitosan into a biofunctional oligosaccharide at a high level.