抄録
Characterization was investigated on the 38 kDa and 42 kDa chitinase (EC3.2.1.14) isozymes from the liver of Japanese common squid Todarodes pacificus. Optimum pH toward colloidal chitin was observed at pH 3.0 for the 38 kDa chitinase, and pH 3.0 and 9.0 for the 42 kDa chitinase. Km and kcat of the 38 kDa and 42 kDa chitinases toward a longer substrate, glycol chitin, were 0.071 mg/mL and 1.22/s, and 0.074 mg/mL and 0.196/s, respectively. Alternatively, strong substrate inhibition of both chitinases were observed toward a short substrate, N-acetylchitopentaose (GlcNAc5). Both chitinases decomposed not only chitin but also chitosan (D. A. 95%). The cleavage pattern and reaction rate were investigated using N-acetylchitooligosaccharides (GlcNAcn, n=2-6). Both chitinases hydrolyzed GlcNAcn (n=4, 5, and 6). The release of GlcNAc was not observed. The speed of the reaction was observed to be in the following order: GlcNAc4>GlcNAc5>GlcNAc6 for the 38 kDa chitinase, and GlcNAc6>GlcNAc5>GlcNAc4 for the 42 kDa chitinase. Both the chitinases released p-nitrophenol from p-nitrophenyl GlcNAcn (n2, 3, and 4). N-terminal amino acid sequences of the 38 kDa and 42 kDa chitinases were YLLSXYFTNWSQYRPGAGKYFPQNI and EYRKVXYYTNWSQYREVPAKFFPEN, respectively.
