ICChI, a glycosylated chitinase from the latex of Ipomoea carnea

Abstract

A multi-functional enzyme ICChI with chitinase/lysozyme/exochitinase activity from the latex of Ipomoea carnea subsp. fistulosa was purified to homogeneity using ammonium sulphate precipitation, hydrophobic interaction and size exclusion chromatography. The enzyme is glycosylated (14–15%), has a molecular mass of 34.94 kDa (MALDI–TOF) and an isoelectric point of pH 5.3. The enzyme is stable in pH range 5.0–9.0, 80 °C and the optimal activity is observed at pH 6.0 and 60 °C. Using p-nitrophenyl- N-acetyl-β- d-glucosaminide, the kinetic parameters K m, V max, K cat and specificity constant of the enzyme were calculated as 0.5 mM, 2.5 × 10 −8 mol min −1 μg enzyme −1, 29.0 s −1 and 58.0 mM −1 s −1 respectively. The extinction coefficient was estimated as 20.56 M −1 cm −1. The protein contains eight tryptophan, 20 tyrosine and six cysteine residues forming three disulfide bridges. The polyclonal antibodies raised and immunodiffusion suggests that the antigenic determinants of ICChI are unique. The first fifteen N-terminal residues G–E–I–A–I–Y–W–G–Q–N–G–G–E–G–S exhibited considerable similarity to other known chitinases. Owing to these unique properties the reported enzyme would find applications in agricultural, pharmaceutical, biomedical and biotechnological fields.