Fig. 4
Fourier transform infrared (FTIR) spectra of the amide I band for two-day old preparations a 12C = O (non-isotopically enhanced) B-YL, b 13C = O N-terminal helical domain of labeled B-YL (amino acid residues: L10/A13/L14/I15/I18/A20) and c 13C = O C-terminal helical domain labeled B-YL (amino acid residues: L32/V33/L36/V37). Synthetic surfactant samples stored at 5 °C for 3 years d 12C = O (non-isotopically enhanced) B-YL, e 13C = O N-terminal helical domain of labeled B-YL (amino acid residues: L10/A13/L14/I15/I18/A20) and f 13C = O C-terminal helical domain labeled B-YL (amino acid residues: L32/V33/L36/V37). Peptides were formulated by co-solvating with surfactant lipids (DPPC:POPC:POPG, 5:3:2 mol:mole) at a ratio of peptide to lipid of 1:10 mol:mole, freeze dried and dispersed into multilamellar vesicles in PBS buffer as detailed in Methods. After storage of the formulated synthetic surfactant for a given period of time, a sample of the dispersion was dried onto the germanium ATR sample plate with a stream of dry nitrogen gas. The dry peptide-lipid film was then hydrated by passing nitrogen gas saturated with D2O for one hour before spectral measurements