Bamberg, E., Apell, H. J., & Alpes, H. (1977). Structure of the gramicidin A channel:
Discrimination between the πL,D and the β helix by electrical measurements with lipid bilayer membranes.
Proceedings of the National Academy of Sciences of the United States of America, 74(6),
2402-2406. doi:10.1073/pnas.74.6.2402.