Oxidation of tyrosine: Antioxidant mechanism of l-DOPA disclosed.

Tyrosine is an amino acid related to crucial physiological events and its oxidation, that produce beneficial or detrimental effects on biological systems, has been extensively studied. Degradation of tyrosine often begins with the loss of an electron in an electron transfer reaction in the presence of a suitable electron acceptor. The reaction is facilitated by excited states of the acceptor in photosensitized processes. Several products of tyrosine oxidation have been described, the main ones being 3,4-dihydroxy- l -phenylalanine (commonly known as DOPA) and tyrosine dimers. Here, we report tyrosine recovery from tyrosyl radical, after one-electron oxidation, in the presence of DOPA. We propose that under high oxidative stress the oxidation of tyrosine may be controlled, in part, by one of its oxidation products. Also, we present strong evidence of antioxidant action of DOPA by preventing tyrosine dimerization, one of the most serious oxidative protein modifications, and the origin of structural modifications leading to the loss of protein functionality. [Display omitted] • DOPA acts as an electron donor to tyrosyl, preventing its further oxidation. • Tyr dimerization is prevented by the presence of DOPA. • DOPA is generated in the reaction between tyrosyl and superoxide anion. • Dopachrome is a secondary product of tyrosine photosensitized oxidation. • Superoxide anion recovers both tyrosine and DOPA after one-electron oxidation. [ABSTRACT FROM AUTHOR]