Antihypertensive effect and purification of an ACE inhibitory peptide from sea cucumber gelatin hydrolysate

Gelatin from the sea cucumber (Acaudina molpadioidea) was hydrolyzed sequentially with bromelain and alcalase. The hydrolysate was fractionated into three ranges of molecular weight (GH-I, <10 kDa; GH-II, <5 kDa; GH-III, <1 kDa) using an ultrafiltration membrane bioreactor system. The GH-III brought about a high angiotensin-I-converting enzyme (ACE) inhibitory activity, with IC₅₀ value of 0.35 mg/ml. An ACE inhibitory peptide was isolated from the GH-III, using the chromatographic methods including ion-exchange chromatography, gel filtration and reversed phase high-performance liquid chromatography. The purified ACE inhibitory peptide with a molecular weight of 840 Da consisted of five main amino acids (Glu, Asp, Pro, Gly and Ala), and its IC₅₀ value was 0.0142 mg/ml. This sea cucumber gelatin hydrolysate (GH-III) was used as drinks administered to renal hypertensive rats (RHR) for 1 month. The systolic blood pressure and diastolic blood pressure of the RHR were significantly reduced, which indicates an antihypertensive effect by oral administration.