Chitinase from Enterobacter sp. NRG4: Its purification, characterization and reaction pattern

Abstract

Enterobacter sp. NRG4 was shown to excrete chitinase into the culture supernatant when cultivated in medium containing chitin. A 60 kDa extracellular chitinase was purified to homogeneity and characterized. The enzyme hydrolyzed swollen chitin, colloidal chitin, regenerated chitin and glycol chitin but did not hydrolyze chitosan. The chitinase exhibited K_m and V_max values of 1.43 mg ml^-1 and 83.33 µM µg^-1 h^-1 for swollen chitin, 1.41 mg ml^-1 and 74.07 µM µg^-1 h^-1 for colloidal chitin, 1.8 mg ml^-1 and 40 µM µg^-1 h^-1 for regenerated chitin and 2.0 mg ml^-1 and 33.33 µM µg^-1 h^-1 for glycol chitin, respectively. The optimal temperature and pH for activity were 45ºC and pH 5.5, respectively. Mg²⁺, K⁺ and Ca²⁺ stimulated chitinase activity by 13, 16 and 18%, respectively whereas Cu²⁺, Co²⁺, Ag⁺ and Hg²⁺ inhibited chitinase activity by 9.7, 15, 22 and 72.2%, respectively at 1 mM concentration. N-bromosuccinamide (NBS) at 1 mM and iodoacetamide at 10 mM concentration completely inhibited the enzyme activity. Dithiobisnitrobenzoic acid (DTNB) at 10 mM concentration inhibited chitinase activity by 97.2%. Chitin was hydrolyzed to chitobiose and N-acetyl D-glucosamine when incubated with the purified enzyme. The hydrolysis pattern of the purified enzyme indicated that the chitinase was an endochitinase.