Consequences of introducing a disulfide bond into an antibacterial and hemolytic peptide

: The effect of introducing a disulfide bridge between the N‐ and C‐terminal ends on the structure and biological activities of the 13‐residue linear peptide PKLLKTFLSKWIG(SPFK), which has both antibacterial and hemolytic activity, have been investigated. The terminal amino acids P and G in SPFK were replaced by cysteines to form a disulfide bridge. The linear peptides C(Acm)KLLKTFLSKWIC(Acm) and C(Acm) KLLKTFLSKWIC(Acm)‐amide, where Acm is acetamidomethyl group, showed antibacterial activity but did not possess hemolytic activity unlike SPFK. Introduction of an S–S bridge resulted in enhanced hemolytic activity compared with SPFK. The hemolytic activity was particularly pronounced in the cyclic peptide CKLLKTFLSKWIC‐amide. Circular dichroism studies indicate that the cyclic peptides tend to adopt distorted helical structures. The cyclic peptides also have a greater affinity for lipid vesicles, which could be the reason for the effective perturbation of the erythrocyte membrane.