Purification and biochemical characterization of an extracellular fructosyltransferase enzyme from Aspergillus niger sp. XOBP48: implication in fructooligosaccharide production

Abstract

An extracellular fructosyltransferase (Ftase) enzyme with a molar mass of ≈70 kDa from a newly isolated indigenous coprophilous fungus Aspergillus niger sp. XOBP48 is purified to homogeneity and characterized in this study. The enzyme was purified to 4.66-fold with a total yield of 15.53% and specific activity of 1219.17 U mg−1 of protein after a three-step procedure involving (NH4)2SO4 fractionation, dialysis and anion exchange chromatography. Ftase showed optimum activity at pH 6.0 and temperature 50 °C. Ftase exhibited over 80% residual activity at pH range of 4.0–10.0 and ≈90% residual activity at temperature range of 40–60 °C for 6 h. Metal ion inhibitors Hg2+ and Ag+ significantly inhibited Ftase activity at 1 mmol concentration. Ftase showed Km, vmax and kcat values of 79.51 mmol, 45.04 µmol min−1 and 31.5 min−1, respectively, with a catalytic efficiency (kcat/Km) of 396 µmol−1 min−1 for the substrate sucrose. HPLC-RI experiments identified the end products of fructosyltransferase activity as monomeric glucose, 1-kestose (GF2), and 1,1-kestotetraose (GF3). This study evaluates the feasibility of using this purified extracellular Ftase for the enzymatic synthesis of biofunctional fructooligosaccharides.