4-hydroxyacetophenone monooxygenase () is an enzyme that catalyzes the chemical reaction:
The four substrates of this enzyme are piceol (4-hydroxyacetophenone), reduced nicotinamide adenine dinucleotide phosphate (NADPH), oxygen, and a proton. Its products are hydroquinone monoacetate, oxidised NADP<sup>+</sup>, and water.
This enzyme is a flavoprotein of Baeyer-Villiger monooxygenase type, which uses molecular oxygen as oxidant and incorporates one of its atoms into the starting material. The systematic name of this enzyme class is (4-hydroxyphenyl)ethan-1-one,NADPH:oxygen oxidoreductase (ester-forming). This enzyme is also called HAPMO. It participates in bisphenol a degradation.