• cofactor
• L-phenylalanine ⇌ {\displaystyle \rightleftharpoons } trans-cinnamate + NH3 The cofactor 3,5-dihydro-5-methyldiene-4H-imidazol-4-one (MIO) is involved in the reaction and sits atop the positive pole of three polar helices in the active site, which helps to increase its electrophilicity. (wikipedia.org)
• Because the mechanism involves a Fe(IV)=O (as opposed to a peroxypterin) hydroxylating intermediate, oxidation of the BH4 cofactor and hydroxylation of phenylalanine can be decoupled, resulting in unproductive consumption of BH4 and formation of H2O2. (wikipedia.org)