Purification of recombinant human POR and P450 17A1. Panel A, SDS-PAGE of N-27 POR-G3H6 preparation in crude lysate (lane 1), after ammonium sulfate precipitation (lane 2), after affinity chromatography (lane 3), and final preparation after Octyl-Sepharose (lane 4). Panel B, UV-visible spectrum of final N-27 POR preparation. Panel C, SDS-PAGE of P450 17A1-H6 preparation in crude solubilized lysate after ultracentrifugation (lane 1), after affinity chromatography (lane 2), after Octyl-Sepharose (lane 3), control P450 17A1 standard (lane 4), and final preparation after hydroxyapatite column (lane 5). Panel D, CO-reduced difference spectrum of purified P450 17A1 shows negligible P420.