Structures and properties of antioxidative peptides derived from royal jelly protein

We previously reported that royal jelly proteins (RJPs) hydrolyzed with protease N show the strong antioxidative activity against the peroxidation of linoleic acid. In this study, 29 antioxidative peptides were isolated from hydrolysate by membrane ultrafiltration, anion-exchange chromatography, gel filtration chromatography, and reverse-phase high performance liquid chromatography. We particularly focused on 12 small peptides with 2–4 amino acid residues: these structures were identified as Ala-Leu, Phe-Lys, Phe-Arg, Ile-Arg, Lys-Phe, Lys-Leu, Lys-Tyr, Arg-Tyr, Tyr-Asp, Tyr-Tyr, Leu-Asp-Arg, Lys-Asn-Tyr-Pro. Analysis of the antioxidative properties of these peptides revealed strong hydroxyl radical scavenging activity, but neither metal-chelating activity nor superoxide-anion radical scavenging activity differed significantly among these peptides. Moreover, three dipeptides (Lys-Tyr, Arg-Tyr, and Tyr-Tyr) containing Tyr residues at the C-terminal had strong hydroxyl-radical and hydrogen-peroxide scavenging activity. This suggests that the antioxidant properties of these peptides are due to a combination of these abilities to act as free-radical scavengers. Three tyrosyl dipeptides containing Tyr residues at their C-termini (Lys-Tyr, Arg-Tyr, and Tyr-Tyr) have phenolic hydroxyl groups, which scavenge the free radicals via the mechanism of donating a hydrogen atom from their hydroxyl group.