11. The 11th amino acid in these chains leads to the three different types of gramicidins . 12. Thus, ions moving through the gramicidin pore carry along a single file of water molecules. 13. This channel shows discrete conductance but different ion selectivity than wild type gramicidin in voltage-clamp experiments. 14. In earlier work with Rene J . Dubos, Hotchkiss helped to develop two antibiotics, gramicidin and tyrocidine. 15. There exist valine and isoleucine variants of all three gramicidin species, and'X'can be either. 16. Y determines which is which; as Y gramicidin A contains tryptophan, B phenylalanine, and C tyrosine. 17. Like valinomycin and nonactin, the gramicidin channel is selective for potassium over sodium, but only slightly so. 18. It has also been noted that the amino acids that are in Gramicidin B are solely hydrophobic amino acids. 19. That gramicidin D functions as a channel was demonstrated by Hladky and Haydon, who investigated the unitary conductance of the channel. 20. Gramicidin B makes up 6 % of Gramicidin D while Gramicidin A and C make up 80 % and 14 % respectively.
