The pooled fractions were loaded onto a desalting column and buffer exchanged into S-loading buffer (50 mM Bis-Tris pH 6.5, 1 mM EDTA, 3 mM DTT, and 10% glycerol). This solution was then loaded at 1.5 mL/min onto the equilibrated HiTrap™ SP HP column. The column was washed with the loading buffer until Abs280nm baselined, then eluted with S-elution buffer containing 500 mM NaCl, 50 mM Bis-Tris pH 6.5, 1 mM EDTA, 3 mM DTT, and 10% glycerol. Fractions with absorbance at 280 nm were collected and assayed for activity with pNPP, the fractions that showed activity were checked for purity on a 15% SDS-PAGE gel.