Protopine 6-monooxygenase () is an enzyme that catalyzes the chemical reaction
The three substrates of this enzyme are protopine, reduced nicotinamide adenine dinucleotide phosphate (NADPH), and oxygen. ts initial benzylisoquinoline alkaloid product is 6-hydroxyprotopine but this spontaneously forms dihydrosanguinarine. NADP<sup>+</sup> and water are the by-products.
The systematic name of this enzyme class is protopine,NADPH:oxygen oxidoreductase (6-hydroxylating). It is also called protopine 6-hydroxylase.