Gramicidin A(11029-61-1), a hydrophobic linear polypeptide, forms channels in phospholipid membranes that are specific for monovalent cations.
Gramicidin A(11029-61-1) is a 15-amino acid linear peptide, 8 of which  are L-amino acid, the other are D-amino acids. It has a hydrophobic side chain, two molecules form a transmembrane channel, which  is a kind of channel-forming ionophore.  It can selectively make the monovalent cation pass through the membrane along the electrochemical gradient, but it does not significantly increase the transport speed. Cations that can be transported by Gramicidin A(11029-61-1) are as follow: H +> NH4 +> K +> Na +> Li +.
The molecular structure of Gramicidin A(11029-61-1):

Gramicidin A(11029-61-1), antibiotic , any of a variety of substances, usually obtained from microorganisms, that inhibit the growth of or destroy certain other microorganisms. Types of antibiotics obtained from the bacterial species Bacillus brevis, which is found in soil. Gramicidin A(11029-61-1) is particularly effective against gram-positive bacteria (see Gram's stain), laboratory staining technique that distinguishes between two groups of bacteria by the identification of differences in the structure of their cell walls. Because the drug is highly toxic, it cannot be administered internally and so is used only on the skin as a lotion or ointment. It is used primarily in the treatment of infected surface wounds, and in eye, nose, and throat infections. In 1939 the American microbiologist René Dubos isolated the substance tyrothricin and later showed that it was composed of two substances, gramicidin and tyrocidine. These were the first antibiotics to be manufactured commercially.

Poison by intravenous and intraperitoneal routes. Moderately toxic by ingestion. An antibiotic. When heated to decomposition it emits toxic fumes of NO_x.