SDS-PAGE of cell supernatant and Ni-NTA agarose-purified PGH. Histidine-tagged PGH was purified with Ni-NTA agarose, and samples of the cell supernatant and purified enzyme were subjected to electrophoresis on a 7.5% ready-made gel and stained as described in Materials and Methods. Lane 1, supernatant (5 μg); lane 2, purified PGH (1 μg); lane 3, Mark12 Unstained Protein Standards (Invitrogen, Carlsbad, CA). Molecular masses in kilodaltons are indicated on the right.