Identification and partial characterisation of a chitinase from Nile tilapia, Oreochromis niloticus

Measurement of chitinase activity in extracts from stomach, intestine, and serum of Nile tilapia with the artificial substrates 4-methylumbelliferil β-d-N,N′-diacetylchitobioside and 4-methylumbelliferil β-d-N,N′Nʺ-triacetylchitotrioside (4MU[GlcNAc]2,3) showed that an endochitinase was involved in the liberation of the fluorophore 4-methylumbelliferone (MU). Enzymes were isolated from tilapia serum by a combination of gel filtration, ion exchange, and reverse-phase chromatography. The molecular mass of the enzyme was estimated to be 75 kDa by SDS-PAGE, suggesting that the enzyme occurs as a monomer. The partially purified enzyme showed maximal activity at pH 7.0 when assayed with 4MU[GlcNAc]2 and lost its activity below pH 5.0 and above pH 8.0. The optimal pH of the purified enzyme toward the substrate 4MU[GlcNAc]3 was pH 9.0 and activity was lost below pH 8.0 and above pH 9.0. Our study has revealed the presence of a chitinolytic enzyme in the gastrointestinal tract and serum that may play a role in digestion and/or defense.