SDS-PAGE of samples from the stages in purification of 4-hydroxyacetophenone monooxygenase. Lane a, crude extract (20 μg); lane b, protein after Q-Sepharose FF chromatography (10 μg); lane c, pure enzyme (7 μg); lane d, high-molecular-weight markers; lane e, pure enzyme (3.5 μg); lane f, low-molecular-weight markers.