1.1.1.116 - 1.1.1.116 col-16a 1.1.1.116 mutants col-15a 1.1.1.116 native enzyme to near homogeneity 1.1.1.116 partial 1.1.1.116 recombinant His6-tagged Ara2p from Escherichia coli by anion exchange and nickel affinity chromatography to homogeneity