The structure of ancovenin, enzyme, was determined to be a unique residues including dehydroalanine and Fujirebio Inc., Ube, Yamaguchi 759-02, Japan a new peptide inhibitor of angiotensin I converting tricyclic peptide which comprises sixteen amino acid three sulfide amino acids as unusual components. Ancovenin, a new peptide inhibitor of angiotensin I converting enzyme (ACE), was isolated from a culture broth of Streptomyces sp. No. A647P-2 in a soil sample collected at Hachioji, Tokyo? The IC,, value of ancovenin to rat lung ACE was obtained to be 8.7 x 10e7 M. Ancovenin is more active than potentiator C2) (2.4 x 10v6 M), one of the known peptide ACE inhibitor, whereas less active than a synthetic antihypertensive agent captopri13) (2.9 x lo-* M). istence of 3MeCys(Hpr) in the hydrolyzate of the product. This result clearly indicated that Abull should be connected with Ala5 (bridge [A]) and, therefore, Ala' with Abu'*. Thus, the primary structure of ancovenin was decided as depicted in Fig. 3. Stereochemistry of the constituent amino acids was satisfactorily studied by gas chromatographic determination of the enantiomers of amino acids. Acid hydrolyzate of ancovenin or desulfurized ancovenin 4 was treated with HCl/i-PrOH and then (TFA)20 to convert each amino acid into TFA-amino acid isopropyl ester. 7, The mixture was gas-chromatographed on glass capillary column coated with chiral stationary phase.') Based on this experiment, we could deduce that one Ala residue and two Abu residues belonging to meso-Lan and three-B-MeLan are of p-form, whereas all other amino acid residues are of L-forms. Therefore, both three-@MeLan residues must have the form of L-AILSD-_Abu. According to the DNS-diastereomer method,g) two Ccr-configurations in meso-Lan were assigned to be o-Al&&la14. As described above, we could determine the whole structure of new ACE inhibitor ancovenin. Peptide antibiotics nisin and subtilin have been already known as cyclic peptides comprising sulfide ring. Ancovenin is therefore the third cyclic sulfide peptide so far clarified. However, a feature of triply overlapped ring system in ancovenin is very unique and peculiar in comparison with those of nisin5c'd) and subtilin . 5e) From this point of view, a study of structure and activity relationship of ancovenin seems to be particularly interesting and important.