Abstract: Porphyra haitanesis was hydrolyzed with AS.1398 neutral protease, and the hydrolysate was filtrated sequentially through ultra-filtration membranes with molecular weight cutoff (MWCO) 2000 D and 8000 D to obtain the fraction with the highest ACE-inhibitory activity, of which the molecular weight was below 2000 D. The fraction was then purified by Sephadex G-15 gel permeation chromatography into 6 peaks, in which peak E had the strongest ACE inhibitory activity with an IC50 of 0.67 mg/mL, and peak E was further fractionated by RP-HPLC to obtain peak No.6 with the highest ACE-inhibitory activity, reaching up to 89.54%. In the end, peak No.6 was injected into RP-HPLC system once again, and two protein peaks were observed in the chromatogram, suggesting that peak No.6 is not a single component and is still in need of further purification. The amino acid composition of peak No.6 was mainly composed of Tyr, Val and Phe. Meanwhile, the MALDI-TOF-MS spectrum of peak No.6 displayed 8 major proton peaks, the peak with the strongest signal intensity was m/z 861.17, and 4 of them were fluctuated around m/z 860, indicating that the mean molecular weight of peak No.6 is approximately 860 D. We speculated that antihypertensive peptides derived from Porphyra haitanensis consisted of 3 Val residues, 2 Phe residues and 1 Tyr residue, of which at the N-terminal Val was located, and that the number of possible ranking sequences was 18.

Key words: Porphyra haitanensis, antihypertensive peptide, isolation, purification, molecular weight