Structure-function relationships of hydroxyl radical scavenging and chromium-VI reducing cysteine-tripeptides derived from rye secalin

The aim of the study was to determine the activity of four rye peptides and molecular descriptors responsible for the detected biological function. The activity was determined using hydroxyl radical scavenging and chromium-VI (Cr(VI) reducing assays while the density functional theory (DFT) was used for molecular descriptors (i.e. structure-activity relationships). It was found that at pH 7.4, peptide CQV had the highest Cr(VI) reducing activity (76%) followed by QCA (30.8%) while other peptides had less than 25% reduction. All tested peptides were less active at pH 3.0 and this was due to poor spatial proximity of thiol and amine on the glutamine side chain. In the hydroxyl radical scavenging assay, CQV had the highest activity with 28.9 +/- 1.3% inhibition of the formation of HO center dot radicals compared to 19.0-13.6% for other peptides. Cysteine at the N-terminal was important for both the reduction of chromium (pH 7.4) and the HO center dot activity because S-H bond energies at that position were lower based on DFT calculations.