The oxidation of tyramine, tyrosine, and related compounds by peroxidase.

Horse-radish peroxidase in the presence of hydrogen peroxide has been reported to act directly upon tyrosine, tryptophan, and cystine, but no reaction products have thus far been identified (I). Tyrosine is of special interest since it has been suggested (1, 2) that the inactivation of certain biologically active proteins by peroxidase depends in part upon oxidation of tyrosyl groups present in the protein. In this investigation, the first reaction product of tyramine, horse-radish peroxidase, and hydrogen peroxide has been shown to be 2,2’-dihydroxy-5,5’-bis(&ethylamino) diphenyl (I), referred to as dityramine. Tyrosine undergoes a similar oxidation to form dityrosine as indicated by chromatographic, ultraviolet absorption and fluorescence data. Both products are chemically analogous to di-p-cresol (2,2’-dihydroxy-5,5’-dimethyldiphenyl) isolated by Westerfeld and Lowe (3) from the reaction of p-cresol, peroxidase, and hydrogen peroxide. Prolonged action by peroxidase upon tyramine or tyrosine yields further reaction products, including a possible triphenyl derivative, and a brown amorphous pigment as an end product. Tyramine + (Compounds I, II, and III) -+ Pigment