Purification and characterisation of angiotensin I converting enzyme inhibitory peptides from lysozyme hydrolysates

Hen egg white lysozyme (HEWL) was hydrolysed with trypsin, papain and a combination of the two. The prepared hydrolysates exhibited ACE inhibitory activity. The hydrolysates were fractionated using ultrafiltration and reverse phase-high performance liquid chromatography (RP-HPLC). Three fractions, which showed the highest ACE inhibitory activities, were purified by RP-HPLC. They were the F7 (from papain–trypsin hydrolysate), F8 (from papain hydrolysate) and F3 (from trypsin hydrolysate) fractions. The IC50 values were 0.03, 0.155 and 0.23 mg/ml for F7, F8 and F3, respectively. The F7 fraction was the most potent ACE inhibitor peptide, and was composed of 12 amino acids, Phe-Glu-Ser-Asn-Phe-Asn-Thr-Gln-Ala-Thr-Asn-Arg (MW: 1428.6 Da). Lineweaver–Burk plots suggest that the F7 peptide acts as an uncompetitive inhibitor against ACE. The kinetic parameters (Km, Vmax, and Ki) for the F7 peptide were measured and compared to the control.