Purification and identification of antihypertensive peptides from seaweed pipefish (Syngnathus schlegeli) muscle protein hydrolysate

Angiotensin-I-converting enzyme (ACE-I) inhibitory peptides were purified from the seaweed pipefish muscle protein using papain, alcalase, neutrase, pronase, pepsin and trypsin. Among them, the alcalase hydrolysate exhibited the highest ACE-I inhibitory activity. The alcalase hydrolysate was separated into four fractions (Fr1, Fr2, Fr3, and Fr4) by fast protein liquid chromatography (FPLC) on a Hiprep 16/10 DEAE FF anion exchange column. Among four fractions, Fr3 has shown the highest ACE-I inhibitory activity and it was further purified into three fractions (Fr3-I, Fr3-II, and Fr3-III) using reverse-phase high performance liquid chromatography (RP-HPLC) on a Primesphere 10 C18 (20 × 250 mm) column. The Fr3-II has exhibited the highest ACE-I inhibition (IC50, 0.62 mg/ml) than the Fr3-III (IC50, 1.44 mg/ml). The amino acid sequences of the obtained peptides from Fr3-II and Fr3-III were identified as Thr-Phe-Pro-His-Gly-Pro (MW, 744 Da) and His-Trp-Thr-Thr-Gln-Arg (MW, 917 Da) respectively. Furthermore, cell viability assay showed that no cytotoxicity of alcalase hydrolysate on human lung fibroblasts cell line (MRC-5). These results suggest that peptides derived from seaweed pipefish can be developed as antihypertensive ingredients in functional foods.