Biochemical properties of an extracellular beta-D-fructofuranosidase II produced by Aspergillus phoenicis under Solid-Sate Fermentation using soy bran as substrate

ABSTRACT

The filamentous fungus A. phoenicis produced high levels of beta-D-fructofuranosidase (FFase) when grown for 72 hrs under Solid-State Fermentation (SSF), using soy bran moistened with tap water (10.5 w/v) as substrate/carbon source. Two isoforms (I and II) were obtained, and FFase II was purified 18-fold to apparent homogeneity with 14 percent recovery. The native molecular mass of the glycoprotein (12 percent of carbohydrate content) was 158.5 kDa with two subunits of 85 kDa estimated by SDS-PAGE. Optima of temperature and pH were 55ºC and 4.5. The enzyme was stable for more than 1 hr at 50ºC and was also stable in a pH range from 7.0 to 8.0. FFase II retained 80 percent of activity after storage at 4ºC by 200 hrs. Dichroism analysis showed the presence of random and beta-sheet structure. A. phoenicis FFase II was activated by Mn2+, Mg2+ and Co2+, and inhibited by Cu2+, Hg2+ and EDTA. The enzyme hydrolyzed sucrose, inulin and raffinose. Kd and Vmax values were 18 mM and 189 U/mg protein using sucrose as substrate.