Isolation and identification of an angiotensin I-converting enzyme inhibitory peptide from pearl oyster (Pinctada fucata) shell protein hydrolysate

Pearl oyster (Pinctada fucata) shell is a marine byproduct. In this study, we focused on the extraction of functional peptides from pearl oyster shell protein hydrolysate. Pearl oyster shell protein was hydrolyzed using two types of proteases, Nucleicin and Orientase 22 BF. The hydrolysate by Orientase 22 BF (6 h of reaction time) exhibited the highest angiotensin I-converting enzyme (ACE) inhibitory activity (82.4%, at peptide concentration of 0.25 mg/mL) with 26.0% degree of protein hydrolysis. The crude hydrolysate was extracted with water and fractionated into two segments (named F1 and F2) by gel chromatography on a Sephadex G-25 column. After consecutive purification of F1 through high-performance liquid chromatography (HPLC) on an ODS column twice, a hexapeptide with the sequence Gly-Val-Gly-Ser-Pro-Tyr (MW: 578.7 Da) was identified based on its amino acid sequence and through LC-MS. The final purified peptide exhibited 5.82 mu g/ml of IC50 value of ACE inhibitory activity. Furthermore, Lineweaver-Burk plots suggested that the purified peptide acts as a competitive inhibitor against ACE. The results of this study suggest that pearl oyster shell proteins can be new attractive raw materials for the production of functional foods against hypertension.