Thus transport rates are higher for channels than for carriers. Gramicidin acts as a channel. It is an unusual peptide, with alternating D and L amino acids. The molecule can assume other conformations in organic solvents, including double helical structures. The outer surface of the gramicidin dimer, which interacts with the core of the lipid bilayer, is hydrophobic.
Ions pass through the more polar lumen of the helix.
Drag the image to view the channel from the side, and down its axis. Gramicidin channel activity can be observed if a small number of gramicidin molecules is present in a lipid bilayer separating two compartments containing salt solution. Each fluctuation, attributed to opening or closing of one gramicidin channel, is the same magnitude. The current increment corresponds to the current flow through a single channel. At right is a drawing - not actual data.