Involved in the biosynthesis of the enzyme cofactor mycofactocin (MFT). Catalyzes the oxidative deamination of AHDP (3-amino-5-[(4-hydroxyphenyl)methyl]-4,4-dimethyl-2-pyrrolidin-2-one), forming an alpha-keto amide moiety on the resulting molecule, which is called pre-mycofactocin (PMFT). This reaction occurs via a 5-[(4-hydroxyphenyl)methyl]-3-imino-4,4-dimethylpyrrolidin-2-one intermediate, which converts to PMFT. The alpha-keto amide moiety is the redox-active center for the redox activity of mycofactocin. 3-amino-5-[(4-hydroxyphenyl)methyl]-4,4-dimethyl-2-pyrrolidin-2-one + H2O + O2 = H2O2 + NH4(+) + pre-mycofactocin Belongs to the FMN-dependent alpha-hydroxy acid dehydrogenase family.