The active fractions were pooled (ranging from 30-40 mL) and concentrated to <12 mL, loaded onto a pre-equilibrated HiLoad 26/60 Superdex 200 prepgrade column (GE) and purified using 10 mM Tris buffer pH 7.5, with 25 mM NaCl, 0.2 mM EDTA, and 3 mM DTT. Fractions were assayed with pNPP for activity and for purity on a 15% SDS-PAGE gel. Pure protein was concentrated to 10-35 mg/mL, and either immediately used for crystallization experiments or diluted with 10% glycerol and frozen with liquid nitrogen and stored at -80°C in aliquots.