Abstract: In order to study the in vivo antioxidant mechanism of two bioactive peptides I and II from naked oat, their amino acid sequences were determined, their antioxidant activity was evaluated, and their molecular structure, charge distribution, molecular frontier orbital distribution, energy difference (ΔE) and radical Fukui index (f0(r)) were calculated by quantum chemistry to deduce the active sites for antioxidant activity of the two peptides. Furthermore, animal tests were carried out and the experimental results were compared with the calculated ones. The results showed the energy of the highest occupied molecular orbital (EHOMO) of peptide I was higher, and the energy difference between the EHOMO and the energy of the lowest unoccupied molecular orbital (ELUMO) of peptide I was smaller, which proves that this peptide has better electron delocalization performance, more easily loses electrons, and is easier to oxidize and therefore a more potent antioxidant. In addition, according to the f0(r), the active sites of peptide I for free radical reaction were located at the double bonds of the indole ring of tryptopha, the amino groups of phenylalanine and the carboxyl group of leucine, whereas the active sites of peptide II were located at two quanidyl groups of arginine and the carboxyl group of leucine. The results of quantum chemical calculation were consistent with those from the animal tests. It was found that both peptides could effectively remove free radicals D-galactose-induced subacute aging mice, peptide I being more effective than peptide II. These results will be helpful for the development of antioxidant products from naked oat.

Key words: naked oat; peptide; quantum chemical calculation; antioxidant