Evaluation of scavenging rate constants of DOPA and tyrosine enantiomers against multiple reactive oxygen species and methyl radical as measured with ESR trapping method

The scavenging rates of DOPA (dl- and l-3-(3,4-dihydroxyphenyl)alanine) and Tyr (tyrosine (dl- and l-3-(4-hydroxyphenyl)alanine)) against five reactive oxygen species (ROS) and methyl radical were measured with the use of electron spin resonance (ESR) spin-trapping method and the scavenging rate constants of DOPA and Tyr were determined. The scavenging rate constants for multiple active species increased in the order of O₂^- < RO < ¹O₂ < H₃C < HO for Tyr and RO O₂^- < ¹O₂ H₃C < HO for DOPA, and the differences in the radical scavenging abilities for l-enantiomers and dl-mixtures of DOPA and Tyr were shown. Further, based on the redox potentials, we have suggested that the primary chemical process of antioxidant reactions with O₂^- and ¹O₂ can be characterized with the electron transfer of antioxidants (DOPA and Tyr).