Tyrocidine

Tyrocidine is a class of naturally occurring antibiotics produced by some strains of Bacillus brevis.

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Tyrocidines A, B, and C are cyclic decapeptides. The biosynthesis of tyrocidine involves three enzymes. Parts of its sequence are identical to gramicidin S.

Tyrocidine A: D-Phe L-Pro L-Phe D-Phe L-Asn L-Gln L-Tyr L-Val L-Orn L-Leu 
Tyrocidine B: D-Phe L-Pro L-Trp D-Phe L-Asn L-Gln L-Tyr L-Val L-Orn L-Leu 
Tyrocidine C: D-Phe L-Pro L-Trp D-Trp L-Asn L-Gln L-Tyr L-Val L-Orn L-Leu 
Tyrocidine D: D-Phe L-Pro L-Trp D-Trp L-Asn L-Gln L-Trp L-Val L-Orn L-Leu 

Tyrocidine and gramicidin are the constituents of tyrothricin, which was originally isolated by René Dubos in 1939, and was the first commercially produced antibiotic. It is used as a topical application; toxicity prevents systemic use. Dubos's discovery helped revive interest in research on penicillin.

Tyrocidine kills bacteria by interacting with their cytoplasmic membrane and causing leakage of their intracellular content. It also affects intracellular membranes such as those of mitochondria.