SDS-PAGE analysis of the expression of rhP4H. rhP4H is present in the various ammonium sulfate fractions. M: middle molecular weight protein markers; lane 1: supernatant sample of rhP4H after induction; lanes 2–7: reconstituted sample of rhP4H after precipitation with 20%, 30%, 40%, 50%, 60% and 70% ammonium sulfate, respectively.