Methylphloroacetophenone oxidase; part of the gene cluster that mediates the biosynthesis of usnic acid, a dibenzofuran lichen product possessing a broad spectrum of biological activities (PubMed:26895859). Two genes, mpas and mpao, comprise the usnic acid biosynthetic gene cluster with a single post-PKS enzyme, the methylphloracetophenone oxidase (mpao) (PubMed:26895859). The methylphloroacetophenone synthase (mpas) is a non-reducing polyketide synthase that produces methylphloracetophenone from acetate via a methylated tetraketide intermediate (PubMed:26895859). The methylphloroacetophenone oxidase then carries out the oxidative dimerization of methylphloracetophenone to usnic acid (PubMed:26895859). Secondary metabolite biosynthesis. Lichens belonging to usnic acid-containing genera have been used as crude drugs throughout the world (PubMed:25707417). Usnic acid is a potentially interesting candidate for such activities as anti-inflammatory, analgesic, healing, antioxidant, antimicrobial, antiprotozoal, antiviral, larvicidal and UV protection (PubMed:25707417). However, it was shown to be toxic for the liver and to lead to contact allergy (PubMed:25707417). Belongs to the cytochrome P450 family.