C-112

Four angiotensin I-converting enzyme (EC 3.4.15.1) (ACE) inhibitory peptides C105, C107, C111, and C112 were isolated from bonito bowels. C111 was obtained from liver, while the others were from intestine. Their amino acids were sequenced as Ser-Val-Ala-Lys-Leu-Glu-Lys for C105, Ala-Leu-Pro-His-Ala for C107, Gly-Val-Tyr-Pro-His-Lys for C111, and Ile-Arg-Pro-Val-Gln for C112. Their ACE inhibition activities were measured for synthetic peptides. The IC50 of these peptides were estimated to be 82, 79, 1.6, and 1.4 microM, respectively. Carboxyl-terminal amino acid(s) were considered to be essential for their expression of ACE inhibition for C105, C107, and C111, while the amino terminal tripeptide Ile-Arg-Pro of C112 was presumed to inhibit ACE after the removal of a dipeptide from C112 with ACE digestion. Presumed original proteins of these peptides are discussed.