The potential of peptides derived from the chymotrypsin hydrolysate of soft shelled turtle yolk against the Angiotensin I Converting Enzyme

Hypertension is a major cause of mortality in the developing country and affects up to 30% of adult population in the world. The angiotensin-I converting enzyme (ACE) is a key therapeutic target when combating hypertension and it has been studied extensively. The aim of this study was to efficiently screen the ACE inhibitory peptide from soft-shelled turtle yolk (TY) by using the chymotrypsin enzyme. The TY proteins were digested followed by ultrafiltration (MWCO 3 kDa). The resulting hydrolysate was fractionated using reversed phase-high performance liquid chromatography (RP-HPLC) and offline strong cation exchange chromatography (SCX). The inhibitory activities of each fraction were measured using an in vitro ACE inhibitory assay. The peptides in the most active fractions of both RP and SCX separations were characterized by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and database-assisted peptide sequencing. The result showed that KF-11 and KY-10 were simultaneously identified from the best ACE inhibitory RP and SCX fractions. The identities and ACE-inhibitory activities of KF-11 and KY-10 were further confirmed using synthetic peptides.