Tyrocidine is a family of eight cationic cyclic decapeptides produced by Bacillus brevis, a soil microorganism. Tyrocidine was first reported by Dubos in 1941 and was the first commercially available antibiotic, but it was found to have toxicity towards human blood cells and reproductive cells. Tyrocidine can be composed of 4 different amino acid sequences, giving Tyrocide A-D. Tyrocidine is the major component, which also contains gramicidin. Tyrocidine exhibits broad-spectrum activity against Gram-positive and Gram-negative bacteria and is the major component of the Tyrothricin complex.
Tyrocidines A, B, and C are cyclic decapeptides. The biosynthesis of tyrocidine involves three enzymes. Parts of its sequence are identical to gramicidin S. In fact, Tyrothricin was later found ot be a mixture of the peptides gramicidin and tyrocidine.