3.5.4.13 - 3.5.4.13 ammonium sulfate precipitation and DE-52 anion-exchange column chromatography 3.5.4.13 recombinant His6-tagged enzyme from Escherichia coli by nickel affinity chromatography, the protein quickly precipitates at concentration higher than 2 mg/ml 3.5.4.13 recombinant protein