FORMATION OF A HYDROXYL RADICAL FROM RIBOFLAVIN SODIUM-PHOSPHATE BY PHOTO-ILLUMINATION

Photo-illumination of riboflavin sodium phosphate (Rp) with phenylalan ine produced significant levels of o-tyrosine, m-tyrosine and p-tyrosi ne as hydroxylated products, The hydroxylation of Rp was pH-dependent, and the maximum rate was around pH 4.5, Replacement of air with nitro gen prevented the formation of tyrosine isomers while the addition of superoxide dismutase or catalase to this system prevented hydroxylatio n. The tyrosine formation by the system was significantly prevented by hydroxyl radical (HO .) scavengers such as potassium iodide, potassiu m bromide, thiourea and sodium formate, No free iron and cupric ions w ere detected in the reaction mixture by inductively-coupled plasma ato mic emission spectrometry, The above results suggest that the formatio n of HO . may occur in the photochemical reaction system in the presen ce of Rp under aerobic conditions, and that a superoxide radical and h ydrogen peroxide may be involved in HO . formation.