Designing antioxidant peptides based on the antioxidant properties of the amino acid side-chains.

Amino acids exert characteristic antioxidant activities depending on the properties of their side residues. The hydrophobic residues were effective against peroxyl radical, while acidic residues and their analogs were effective against peroxynitrite. Peptides containing tyrosine showed different activities against different reactive oxygen species (ROS) and/or reactive nitrogen species (RNS). The number and position of tyrosine did not affect the antioxidant activity against hypochlorite ion. Against the peroxyl radical, the number of tyrosine residues affected the antioxidant activity, while its position did not have a significant effect. The tyrosine position was an important factor for the antioxidant activity against peroxynitrite. The peptide GWWW showed higher antioxidant activity against peroxyl radical than tryptophan at concentrations below 25 µM, and high activity against peroxynitrite at 250 µM. Our results suggest that antioxidant peptides against a specific target ROS or RNS can be designed based on the characteristics of the amino acid side chains.