Fig. 3. (a) Sequences of aromatic amino acids containing stapled peptides. (b) Gel retardation assay of siRNA/stEK or aromatic amino acid derivative complexes. The preformed siRNA/CPP complexes were analyzed by electrophoresis on 1% of agarose gel stained with ethidium bromide. siRNA was pre-incubated with peptides for 30 min in 0.5× PBS buffer. (c) Dose-dependent complex formation was determined by assessing unbound band intensities. Plot of siRNA complex formation against the molar ratio of stEK and LKH-stEK peptide shown in (b). (d) Plot of siRNA complex formation against charge ratio (+/–) shown in (b). The respective net charge of each peptide at pH 7.4 was calculated to be 5.99, 3.37, 3.01, and 5.97 for stEK, LKH-stEK, LKpyr-stEK, and LKacr-stEK, respectively using MarvinView software package (free software from ChemAxon).