Structure-function of hydroxyl radical scavenging and chromium-VI reducing cysteinetripeptides derived from rye secalin

This study evaluated for the first time hydroxyl radical scavenging and chromium VI (Cr(VI) reducing properties of four cysteine containing peptides derived from rye secalin. Density functional theory (DFT) calculations were performed to determine the antioxidation mechanism and the effect of residue order. The peptides tested (CQV, QCA, QVC, QCV) were obtained from in silico digestion of rye secalin with Proteinase-K and selected because they contained thiol, a known redox functional group. It was found that at pH 7.4, CQV had the highest Cr(VI) reducing activity (76 %) followed by QCA and QCV (30.8 and 25.5 %, respectively). QVC and GSH had similar but lower activities (11.3 and 11.7%). At pH 3.0, CQV and QCV were found to be less active than the other two peptides. In the hydroxyl radical scavenging assay, CQV had the highest activity with 28.9 ± 1.3 % inhibition of the formation of HO• radicals compared to 19.0 – 13.6% for other peptides. The highest reactivity of CQV with Cr(VI) under neutral conditions was due to the proximity of thiol and amine of glutamine that allowed the formation of a transition state that facilitated the reduction. Cysteine at the N-terminal was important for both the reduction of chromium (pH 7.4) and the HO• scavenging activity because the S-H bond at that position was found by the DFT analysis to have the lowest bond dissociation energy.