Riboflavin sensitized photooxidation of tyrosine

The oxygen reactive species generated during the photooxidation of tyrosine sensitized by riboflavin were studied and the products formed were isolated. It was found that this process occurs preferently through a type I mechanism, which involves the direct interaction between the excited state of the sensitizer and tyrosine. The formation of O2.-, H2O2 and .OH was detected along the photooxidative process. By changing H2O by D2O it could be established that 1O2 has no significant role in the photooxidation of tyrosine sensitized by riboflavin. When a previously irradiated solution of tyrosine was applied to a Sephadex G-15 column, four fractions could be separated corresponding to products having hydrodynamic volumes larger than those of the reactants. By the use of 14C-tyrosine the aminoacidic origin of the products could be determined; one of them was identified as bityrosine, according to its fluorescence properties and 1H-NMR spectrum.