Isolation of Acein‐2, a novel angiotensin‐I‐converting enzyme inhibitory peptide derived from a tryptic hydrolysate of human plasma

Abstract

We previously described a novel angiotensin‐I‐converting enzyme (ACE) inhibitory peptide, designated Acein‐1, that was isolated from a tryptic hydrolysate of human plasma. We now report a second such inhibitory peptide, Acein‐2 obtained from the same hydrolysate. The peptide was purified by gel filtration and cation exchange chromatography followed by reversed‐phase gradient and isocratic high performance liquid chromatography. Acein‐2 was found to be a tripeptide, Leu‐Ile‐Tyr, which is thought to correspond to f(518–520) of human α2‐macroglobulin. The synthetic tripeptide showed a potent dose‐dependent inhibition of ACE, with an IC₅₀ value of 0.82 μmol/l. Lineweaver–Burk plots suggested that Acein‐2 as well as the previously described Acein‐1 are non‐competitive inhibitors.