Purification of Cr-rPFO on HIS-SelectNickel Affinity Gel. Left panel, SDS-PAGE (10% acrylamide gel) analysis of the purification of Cr-rPFO from E. coli cells. The gel was stained with Coomassie Brilliant Blue. Lane 1, E. coli cells expressing Cr-rPFO; lane 2, E. coli soluble fraction; lane 3, proteins that do not bind on the HIS-Select resin; lane 4, wash with 30 mm imidazole; lane 5, Cr-rPFO elution with 100 mm imidazole (6 µg). Right panel, Cr-rPFO (40 µg) analyzed by blue native-PAGE (5%–15% acrylamide gel) run under an N2 atmosphere. CBB, Gel lane stained with Coomassie Brilliant Blue; NBT, gel lane stained for PFO activity in an assay mixture containing 10 mm nitroblue tetrazolium as electron acceptor.