Gramicidin A (gA) is a linear pentadecapeptide, which exhibits various conformations depending on the environment. The conformational behavior of gA in spherical and rod-shaped cationic micelles formed by cetyltrimethylammonium bromide (CTAB) surfactant has been studied using circular dichroism (CD) and fluorescence spectroscopy, and a probable structure of gramicidin A in CTAB media has been proposed. A CD study shows that gramicidin A assumes beta(6.3) helical structure in cationic spherical as well as rod-shaped CTAB micellar media. Modeling studies show the flexibility of the side chain conformation particularly in tryptophan-9. Study of intrinsic fluorescence of tryptophans in gramicidin A indicates three distinct environments for the four-tryptophan residues in CTAB media.

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