Formation of a hydroxyl radical from riboflavin sodium phosphate by photo-illumination

Photo-illumination of riboflavin sodium phosphate (Rp) with phenylalanine produced significant levels of o-tyrosine, m-tyrosine and p-tyrosine as hydroxylated products, The hydroxylation of Rp was pH-dependent, and the maximum rate was around pH 4.5, Replacement of air with nitrogen prevented the formation of tyrosine isomers while the addition of superoxide dismutase or catalase to this system prevented hydroxylation. The tyrosine formation by the system was significantly prevented by hydroxyl radical (HO .) scavengers such as potassium iodide, potassium bromide, thiourea and sodium formate, No free iron and cupric ions were detected in the reaction mixture by inductively-coupled plasma atomic emission spectrometry, The above results suggest that the formation of HO . may occur in the photochemical reaction system in the presence of Rp under aerobic conditions, and that a superoxide radical and hydrogen peroxide may be involved in HO . formation.