Purification and characterisation of soluble acid invertase from mango fruits

Abstract

AbstractSoluble acid invertase (SAI) was purified from mango fruits (Mangifera indica L.) by ammonium sulphate fractionation and anion‐exchange chromatography (DEAE‐Sepharose Fast Flow). Molecular mass of the enzyme is 45 kDa estimated by SDS–PAGE. Dynamic light scattering analysis suggests the hydrodynamic radius of SAI distributes from 4 to 20 nm with a peak at 6.68 nm. Transmission electron microscopy shows that SAI is a globulin with diameter of 10–30 nm. Its optimal pH and temperature are 4.0 and 60 °C, respectively. The enzyme is not stable at high temperature (≥60 °C) or in alkaline (pH ≥ 8) environment. Using sucrose as substrate, its KM and Vmax are 25.55 mm and 1.002 mmol min−1 mL−1, respectively. Its circular dichroism spectrum shows a negative band at 220 nm and a positive band at 195 nm, suggesting a β‐sheet structure. The fluorescence spectra reflect that the tryptophan and tyrosine residues of SAI are partially exposed.