Levansucrase (ATCC 23350) from B. amyloliquefaciens was
produced and purified through PEG 200 precipitation and
size exclusion chromatography as previously described (Tian &
Karboune, 2012). The resulting purified levansucrase was dialyzed
against 5mM potassium phosphate buffer (pH 6.0) using a membrane
(5 kDa cut-off) for 48 h at 4 ◦C and then freeze-dried. The
total levansucrase activity was assayed using sucrose as substrate
as previously described (Tian & Karboune, 2012). The amount of
released reducing sugars was determined from a standard curve
using glucose (0.5–10 mM). All experiments were assayed in triplicates.
The protein content was measured using the Standard
BioRad (USA) Protein Assay. The concentration of protein was
then estimated from a standard curve using bovine serum albumin
(0.0625–1 mg/mL). The specific activity was expressed as the
mol of released glucose or fructose per minute of reaction and
per mg of protein. The specific activity of LS was estimated at
413.3mol/min/mg proteins.