A pivotal peptide (Ile-Leu-Lys-Pro) with high ACE- inhibitory activity from duck egg white: identification and molecular docking

Abstract Salted duck egg white was desalted and hydrolyzed to produce angiotensin I-converting enzyme (ACE) inhibitory peptides. Single factor test and response surface design were performed to determine the best hydrolysis conditions: enzyme dosage 11875.99 U/g, substrate concentration 33.04 g/L and hydrolysis time 4 h. The fraction V (MW < 1 kDa), which exhibited the strongest ACE inhibitory activity, was characterized by HPLC-ESI-MS/MS. Eighty-three peptides were identified, and among them Ile-Leu-Lys-Pro, Ile-Asn-Ser-Trp, Ile-Arg and His-Pro-Ala were synthesized for further research. Ile-Leu-Lys-Pro exhibited the highest ACE inhibitory activity (IC50: 0.355 mM). The molecular docking studies revealed that nine amino acids contributed to stabilize the docking complex. The ACE inhibition of Ile-Leu-Lys-Pro and Ile-Asn-Ser-Trp were mainly attributed to Ile in N-terminal. The residues Glu362 and Ala332 were the important binding sites in molecular docking. This research expands the understanding of ACE inhibitory peptides from duck egg white as well as highlights an opportunity for recycling an otherwise discarded byproduct.