cyclopeptide

cy·clo·pep·tide

(sī'klō-pep'tīd), One of a group of cyclic peptides that inhibit RNA polymerase and thus block protein synthesis. Used as topical antimicrobials, but toxic if ingested. Constituent in mushrooms that causes toxicity (amatoxin).
See also: polymyxin, amatoxin.

cy·clo·pep·tide

(sī'klō-pep'tīd) A polypeptide lacking terminal -NH2 and -COOH groupsby virtue of their combination to form another peptide link, forming a ring.