The active fractions were pooled and concentrated to <12 mL, loaded onto a pre-equilibrated HiLoad 26/60 Superdex 200 prepgrade column (GE), and purified using 10 mM BisTris buffer pH 6.5, with 25 mM NaCl, 0.2 mM EDTA, and 3 mM DTT. Fractions were assayed with pNPP for activity and purity on a 15% SDS-PAGE gel. Pure protein was concentrated to 10-20 mg/mL and either kept on ice to immediately set up crystal trays or diluted with 10% glycerol and frozen with liquid nitrogen and stored at -80 °C in aliquots.