Angiotensin-Converting Enzyme (ACE) Inhibitory Activities of Protein Hydrolysates from Indonesian Sea Cucumbers

Hypertension is one of the risk factors that contribute significantly to the prevalence of cardiovascular diseases in Indonesia. Peptides have been known to exhibit anti-hypertension activities, thus are potential as an alternative treatment of hypertension. In this study, we collected three species of under-utilized sea cucumbers from Lampung and Gorontalo provinces to explore their hydrolysates as angiotensin-converting enzyme (ACE)-inhibitors. The identification of the collected samples was conducted by a molecular approach. The sea cucumber hydrolysates were produced by using bromelain, alcalase, or the combination of both enzymes. The hydrolysis process was carried out using a 50 mM phosphate buffer at pH 7 with E/S ratio of 1% at 45 degrees C for 24 h. The fractionation of the most active protein hydrolysate was conducted using ultrafiltration membranes with 3, 5, and 10 kDa cut-offs. The results showed that the collected sea cucumbers were identified as Holothuria atra, Holothuria leucospilota, and Bohadschia marmorata, respectively. The ACE inhibitory analysis revealed that the alcalase hydrolysates of H. atra (AHHa) contain the most active ACE inhibitor with an IC50 value of 0.32 mg/mL. Fraction AHHa IV (< 3 kDa) showed the highest inhibition toward ACE compared to the other fractions. The kinetic studies of unfractionated AHHa and AHHa IV indicated that both peptides inhibited ACE in a mixed-inhibition mode. The lower Ki value of unfractionated AHHa peptides than that of AHHa IV, suggesting that the former binds stronger to ACE than the latter.