Molecular design of the antioxidative peptide motif by combinatorial chemistry and its application to food proteins

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We investigated the antioxidative properties of 114 synthetic His- or Tyr-containing peptide libraries, and 108 synthetic peptide libraries, which were designed on basis of antioxidative peptides derived from a proteolytic digest of soybean protein, to explore the antioxidative mechanism and to design the antioxidative peptide motif. Antioxidative activity of the peptide library was screened by high throughput screening assamps on micro titerplates as well as the ferric thiocyanate method. The activity spectrum of the tripeptides obtained from theeasurement of the radical scavenging activity was different from those from the ferric thiocyanate method in the peroxidation of linoleic acid. Pro-His-His which was very potent in the peroxidation of linoleic acid, did not act as a radical scavenger. The tripeptides containing Trp residue in the middle showed higher activity than the peptides containing His residue in the radical scavenging activity. The activities of tripeptides containing Trp or Tyr at the C-terminus were very high. Tyr-His-Tyr had a strong synergistic effect by the combined use with BHA or σ-tocopherol against the peroxidation of linoleic acid. We designed new antioxidant compounds, which were hybrids of peptides and nonpeptidic antioxidants, and measured their radical scavenging activity. The abilities of food protein hydrolysates and synthetic peptides to scavenge the peroxynitrite were also investigated. The tripeptides containing CySH had stronger scavenging activities than the peptides containing Met or other amino aciresidues. The peptides of the same amino acid composition exerted sequence dependent activities. i.e., CySH-Tyr-Tyr and Tyr-Tyr-CySH were more potent than Tyr-CySH-Tyr. Reversed-phase HPLC analysis of the reaction mixture revealed the extensive modification of peptides added.