Purification and the secondary structure of a novel angiotensin I-converting enzyme (ACE) inhibitory peptide from the alcalase hydrolysate of seahorse protein

Abstract

Bioactive peptides with blood pressure-lowering functions have received increasing attention. In recent years, many ACE-inhibiting peptides have been widely purified from various food-derived proteins and have received considerable interest owing to their potential role in cardiovascular diseases and in the reduction of side effects. In this study, we hydrolyzed a three-spot seahorse (Hippocampus trimaculatus Leach) protein by alcalase to obtain a hydrolysate containing angiotensin I-converting enzyme (ACE) inhibitory peptide. Then, the hydrolysate was fractionated by dialysis, Sephadex G-25 gel filtration chromatography, and reverse-phase high performance liquid chromatography. After consecutive purification, a potent ACE-inhibiting peptide composed of 8 amino acids (Pro-Ala-Gly-Pro-Arg-Gly-Pro-Ala; MW: 721.39 Da; IC₅₀ value: 7.90 μM) was successfully isolated from three-spot seahorse protein. For the first time, a novel ACE-inhibiting peptide (PAGPRGPA) was isolated from the seahorse. Circular dichroism (CD) analyses suggested that the secondary structure of the purified peptide was mainly composed of random coil. Therefore, the peptide from seahorse protein may be used as a favorable ingredient in nutraceuticals, medicines, and functional foods against antihypertensive and related diseases.

Keywords: ACE inhibitory peptide; Alcalase; Protein secondary structure; Three-spot seahorse protein hydrolysate.

Fig. 1

Elution profile of the dialysis product by Sephadex G-25 gel filtration chromatography

Fig. 2

Elution profile of fraction F2 by RP-HPLC on a Hypersil™ ODS C₁₈ column (10 mm × 250 mm, 5 μm)

Fig. 3

ESI–MS/MS spectrum of the fraction F2-4 (m/z 721.39)

Fig. 4

Far ultraviolet circular dichroism spectrum of the purified peptide