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A 56 kDa chitinase isozyme (PaChiB) was purified from the stomach of the silver croaker Pennahia argentatus. The optimum pH and pH stability of PaChiB were observed in an acidic pH range. When N-acetylchitooligosaccharides ((GlcNAc)n, n=2 -6) were used as substrates, PaChiB degraded (GlcNAc)4 -6 and produced (GlcNAc)2,3. It degraded (GlcNAc)5 to produce (GlcNAc)2 (23.2%) and (GlcNAc)3 (76.8%). The ability to degrade p-nitrophenyl N-acetylchitooligosaccharides (pNp-(GlcNAc)n, n=2 -4) fell in the following order: pNp-(GlcNAc)3≫ pNp-(GlcNAc)2 pNp-(GlcNAc)4. Based on these results, we concluded that PaChiB is an endo-type chitinolytic enzyme, and that it preferentially hydrolyzes the third glycosidic bond from the non-reducing end of (GlcNAc)n. Activity toward crystalline α- and β-chitin was activated at 124%-185% in the presence of 0.5 M NaCl. PaChiB exhibited markedly high substrate specificity toward crab-shell α-chitin.

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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 (n = 2, 3, and 4). N‐terminal amino acid sequences of the 38 kDa and 42 kDa chitinases were YLLSXYFTNWSQYRPGAGKYFPQNI and EYRKVXYYTNWSQYREVPAKFFPEN, respectively.

Chitin, a linear ƒÀ-1,4 linked polymer of N-acetyl-Dglucosamine, is a common constituent of the exoskeleton of crustaceans and fungal cell walls. The biological decom position of chitin is carried out by a system of endo-type and exo-type enzymes, known as chitinase (EC 3.2.1.14) and ƒÀ-N-acetylhexosaminidase (EC3.2.1.52), respectively.