Purification and Identification of an ACE Inhibitory Peptide from Walnut Protein

In the present study, a novel angiotensin I-converting enzyme (ACE)-inhibitory peptide, P-2a2, was purified to homogeneity from walnut protein hydrolysate by ultrafiltration, consecutive column chromatography, and high-performance liquid chromatography. The purified peptide was characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrophotometry and a liquid-phase peptide sequencer. The molecular mass of P-2a2 was tested to be 1033.42 D. Its amino acid sequence was determined to be Trp-Pro-Glu-Arg-Pro-Pro-Gln-Ile-Pro. The potent ACE-inhibitory peptide is an enneapeptide and shows a high ACE-inhibitory activity, with an IC50 value of 25.67 μg/mL.