Figure 7.

Absorbance measurements from vesicles containing a polyunsaturated lipid exposed to Cu²⁺ and piscidin bound to Cu²⁺. SUVs made of 3:1 DLPC/POPG were prepared and exposed to different forms and amounts of Cu²⁺ and measured by UV spectrophotometry after 24 h of exposure. (A) Samples containing SUVs at a fixed lipid concentration of 0.50 mg/mL (640 µmol/L) were mixed with various amounts of CuCl₂, as follows: Cu²⁺/L = 1:2 molar ratio (black), Cu²⁺/L = 1:8 (red), Cu²⁺/L = 1:32 (blue), BHT/L = 1:100, and Cu²⁺/L = 1:8 (cyan) and lipid alone (magenta). (B) SUVs at a concentration of 0.20 mg/mL (260 µmol/L) were studied in the presence of the peptides at P/L = 1:10, corresponding to a peptide-Cu²⁺ complex concentration of 26 µmol/L. P1-Cu²⁺ (blue, dashed); P3- Cu²⁺ (red, dashed); P1 (blue); P3 (red); lipid alone (black). The source of free Cu²⁺ (CuCl₂) was the same as that used for metallating P1 and P3. Measurements were taken in triplicates at 24 h after exposure. The spectra were corrected for the background signals from CuCl₂ and the lipids at time zero as explained in the Methods. Uncertainties are smaller than the line thicknesses. Strong absorbance at 234 nm after 24 h of exposure points at the formation of lipid oxidation products, a result confirmed by mass spectrometry (Fig. S7).