Reaction pattern of Bacillus cereus D-11 chitosanase on chitooligosaccharide alcohols.

The purified endochitosanase (Mw 41 kDa) from bacterium Bacillus cereus D-11 hydrolyzed chitooligomers (GlcN)5-7 into chitobiose, chitotriose, and chitotetraose as the final products. The minimal size of the oligosaccharides for enzymatic hydrolysis was a pentamer. To further investigate the cleavage pattern of this enzyme, chitooligosaccharide alcohols were prepared as substrates and the end products of hydrolysis were analyzed by TLC and HPLC. The chitosanase split (GlcN)4GlcNOH into (GlcN)3+ (GlcN)1GlcNOH, and (GlcN)5GlcNOH into (GlcN)4+ (GlcN)1GlcNOH and (GlcN)3+(GlcN)2GlcNOH. The heptamer (GlcN)6GlcNOH was split into (GlcN)5 [thereafter hydrolyzed again into (GlcN)3+(GlcN)2]+(GlcN)1GlcNOH, (GlcN)4+(GlcN)2GlcNOH, and (GlcN)3+(GlcN)3GlcNOH, whereas (GlcN)1-3GlcNOH was not hydrolyzed. The monomers GlcN and GlcNOH were never detected from the enzyme reaction. These results suggest that D-11 chitosanase recognizes three glucosamine residues in the minus position and simultaneously two residues in the plus position from the cleavage point.