Gramicidin S or
Gramicidin Soviet is an antibiotic effective against some
Gram positive and
Gram negative bacteria as well as some fungi. It is a derivative of
gramicidin, produced by the
Gram positive bacterium
Bacillus brevis. Gramicidin S is a cyclodecapeptide, constructed as two identical
pentapeptides joined head to tail, formally written as
cyclo(-
Val-
Orn-
Leu-D-
Phe-
Pro-)
2. That is to say, it forms a ring structure composed of five different amino acids, each one used twice within the structure. Another interesting point is that it utilizes two amino acids uncommon in
peptides:
ornithine as well as the atypical
stereoisomer of
phenylalanine. It is synthesized by gramicidin S synthetase.