A novel angiotensin-I-converting enzyme (ACE) inhibitory peptide, designated acein-1, was isolated from the tryptic hydrolysate of human plasma. Gel filtration and cation exchange chromatography were performed to purify this peptide, followed by reversed-phase gradient and isocratic high-performance liquid chromatography. Acein-1 was found to be a heptapeptide, Tyr-Leu-Tyr-Glu-Ile-Ala-Arg, corresponding to f(138^144) of human serum albumin. The synthetic heptapeptide, hexapeptide (Tyr-Leu-Tyr-Glu-Ile-Ala, des-U R acein-1) and octapeptide (Tyr-Leu-Tyr-Glu-Ile-Ala-Arg-Arg, acein-1R) showed dose-dependent inhibitions of ACE, and their IC SH values were 16 W Wmol/l, 500 W Wmol/l and 86 W Wmol/l, respectively. Acein-1 might be a non-competitive inhibitor, while acein-1R may be an uncompetitive inhibitor, as shown by Lineweaver-Burk plots.z 1998 Federation of European Biochemical Societies.

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-IleTyr, which is thought to correspond to f(518^520) of human K K2-macroglobulin. The synthetic tripeptide showed a potent dosedependent inhibition of ACE, with an IC 50 value of 0.82 W Wmol/l. Lineweaver^Burk plots suggested that Acein-2 as well as the previously described Acein-1 are non-competitive inhibitors.z 2000 Federation of European Biochemical Societies.

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