Peptides with angiotensin-I converting enzyme (ACE) inhibitory activity have received considerable interest due to their potential as antihypertensive agents and consumer concern over the safety of synthetic drugs. The objective of this study was to isolate ACE inhibitory (ACEI) peptides from Caulerpa lentillifera (known commonly as sea grape) protein hydrolysate. In this study, short-chain peptides were obtained after hydrolysis by various enzymes and subsequently by ultrafiltration. Thermolysin hydrolysate showed the highest ACEI activity. Bioassay-guided fractionation was performed using reversed-phase high performance liquid chromatography (RP-HPLC) to uncover the fraction 9 with the highest ACE inhibitory activity from thermolysin hydrolysate. Peptides in this fraction were further identified using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis coupled with de novo sequencing, which gave two oligopeptides, FDGIP (FP-5) and AIDPVRA (AA-7). The identities and activities of these two peptides were further confirmed using synthetic peptides. Their IC50 values were determined as 58.89 ± 0.68 µM and 65.76 ± 0.92 µM, respectively. Moreover, the inhibition kinetics revealed that both FP-5 and AA-7 are competitive inhibitors. These activities were further explained using molecular docking simulation. The present study is the first report about ACEI peptides derived from Caulerpa lentillifera and it shows the potential for preventing hypertension and for functional food development.
Keywords: ACE inhibitory peptide; Caulerpa lentillifera; LC-MS/MS; bioassay-guided fractionation; de novo sequencing; sea grapes.