Cyclic peptide chain is present in ?
Gramicidin A
Gramicidin B
Gramicidin D
Gramicidin S
Ans. is d i.e., Gramicidin S Gramicidin Gramicidin is a heterogeneous mixture of three antibiotic compounds, gramicidins A, B and C, making up 80%, 6%, and 14%, respectively,all of which are obtained from the soil bacterial species Bacillus brevis and called collectively gramicidin D. Gramicidin D contains linear pentadecapeptides, that is chains made up of 15 amino acid. This is in contrast to gramicidin S, which is a cyclic peptide chain. Gramicidin is active against Gram-positive bacteria, except for the Gram-positive bacilli, and against select Gram-negative organisms, such as Neisseriabacteria. Its therapeutic use is limited to topical application, as it induces hemolysis in lower concentrations than bacteria cell death, so it cannot be administered internally.