Purification and kinetic characterization of a fructosyltransferase from Aspergillus aculeatus

A fructosyltransferase present in Pectinex Ultra SP-L, a commercial enzyme preparation from Aspergillus aculeatus, was purified to 107-fold and further characterised. The enzyme was a dimeric glycoprotein (20% (w/w) carbohydrate content) with a molecular mass of around 135 kDa for the dimer. Optimal activity/stability was found in the pH range 5.0–7.0 and at 60 °C. It was stable or slightly activated (upto 1.4-fold) in the presence of reducing agents, such as dithiothreitol and 2-mercaptoethanol, and detergents, such as sodium dodecylsulphate and Tween 80. The enzyme was able to transfer fructosyl groups from sucrose as donor producing the corresponding series of fructooligosaccharides: 1-kestose, nystose and fructosylnystose. Using sucrose as substrate, the kcat and Km values for transfructosylating activity were 1.62 ± 0.09 × 104 s−1 and 0.53 ± 0.05 M, whereas for hydrolytic activity the corresponding values were 775 ± 25 s−1 and 27 ± 3 mM. At elevated sucrose concentrations, the fructosyltransferase from A. aculeatus showed a high transferase/hydrolase ratio that confers it a great potential for the industrial production of prebiotic fructooligosaccharides.