we have addressed this question by investigating the permeability characteristics of channels formed by gramicidins where the nh2-terminal amino acid is either phenylalanine or one of a series of substituted phenylalanines : p-hydroxy- , p-methoxy- , o-fluoro- , m-fluoro- , or p-fluorophenylalanine .
C0031453
phenylalanines
C0030137
p-fluorophenylalanine