<jats:title>Abstract</jats:title><jats:p>The screening for growth inhibitors against <jats:italic>Bacillus subtilis</jats:italic> revealed a peptide antibiotic produced by <jats:italic>Streptomyces griseoflavus</jats:italic> TÜ 4072. Very high yields of the antibiotic named aborycin were obtained by cultivation in a medium containing soybean meal and sucrose. Isolation from the mycelium was carried out by a combination of extraction and gel chromatography. Preparative HPLC yielded the uniform antibiotic. The structure elucidation was based on GC amino acid analysis on a chiral phase, automated Edman degradation, electrospray tandem mass spectrometry and two‐dimensional NMR (TOCSY, ROESY, HSQC, HMBC). Aborycin represents a 21‐peptide that is cyclized from the side chain of Asp<jats:sup>9</jats:sup> to the N‐terminus of Cys<jats:sup>1</jats:sup>. Two disulfide bonds Cys<jats:sup>1</jats:sup> to Cys<jats:sup>13</jats:sup> and Cys<jats:sup>7</jats:sup> to Cys<jats:sup>19</jats:sup> form a tricyclic structure consisting exclusively of protein amino acids. The peptide antibiotic aborycin was found to be identical with a HIV protease inhibitor isolated recently from <jats:italic>Streptomyces</jats:italic> SP 9440. <jats:chem-struct-wrap><jats:chem-struct><jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" mimetype="image/gif" position="anchor" specific-use="enlarged-web-image" xlink:href="graphic/must001.gif"><jats:alt-text>magnified image</jats:alt-text></jats:graphic></jats:chem-struct></jats:chem-struct-wrap>