Purification and some properties of β-fructofuranosidase from Aspergillus niger IMI303386

An intracellular β-fructofuranosidase (EC 3.2.1.26) from Aspergillus niger IMI 303386 was purified to homogeneity according to SDS-PAGE by (NH4)2SO4 precipitation, DEAE Sepharose Fast Flow ion-exchange chromatography and Ultrogel AcA44 gelfiltration. This protocol gave 50-fold of purification and 42% recovery of enzyme activity. The molecular mass of β-fructofuranosidase from A. niger was estimated to be in the range from 120 to 130 kDa. This enzyme shows two protein species on isoelectric focusing. The pI value of major and minor protein species was calculated to be 5.4 and 4.4, respectively. Ba2+, Mg2+, Ca2+ and sodium-EDTA are activators, while Hg2+, Ag+ and Ni2+ are strong inhibitors of β-fructofuranosidase. The enzyme is completely stable in the pH range from 4 up to 8 and has a pH optimum of 5.5. The optimum temperature of β-fructofuranosidase was 50 °C and enzyme is stable up to 55 °C. More than 90% of residual activity was retained after 5 h incubation. β-Fructofuranosidase from A. niger IMI 303386 is a glycoprotein with the carbohydrate content of 17%.