KINETICS OF A CHITINASE FROM A PRAWN, PENAEUS-JAPONICUS

Kinetic analysis was done on a chitinase (EC 3.2.1.14) purified from the liver of a prawn, Penaeus japonicus, using N-acetylchitooligosaccharides (GlcNAcn, n = 2 to 6), p-nitrophenyl N-acetylchitooligosaccharides (pNp-GlcNAcn, n = 1 to 5), and colloidal chitin as the substrates. The enzyme hydrolyzed GlcNAc4 to two molecules of GlcNAc2, GlcNAc5 to GlcNAc2 plus GlcNAc3, and GlcNAc6 by two ways to GlcNAc2 plus GlcNAc4 (87%), and two molecules of GlcNAc3 (13%). Neither GlcNAc2 nor GlcNAc3 was hydrolyzed. The Km and kcat were 0.249 mm and 3.38 sec−1 for GlcNAc4,0.018 mm and 2.67 sec−1 for GlcNAc5, and 0.005 mm and 2.72 sec−1 for GlcNAc6, respectively. The cleavage patterns of p-nitrophenyl N-acetylchitooligosaccharides were different from those of the corresponding N-acetylchitooligosaccharides. The enzyme hydrolyzed colloidal chitin to produce mainly GlcNAc2 and a trace of GlcNAc3. Allosamidin inhibited prawn chitinase in a competitive way with a Ki of 0.1 μm and IC50 of 0.14 μm. These results suggest that prawn chitinase is an endo-type chitinolytic enzyme, but different from insect chitinase or yam chitinase in the substrate specificity and cleavage pattern. © 1990 by the Japan Society for Bioscience, Biotechnology, and Agrochemistry.