Spectroscopic Analysis of Tryptophan Residues

The wavelengths of maximum fluorescence (WMF) of the tryptophan (Trp) residues in apoA-I were determined from the uncorrected spectra using an LS55 spectrofluorometer (Perkin-Elmer, Norwalk, CT, USA), as described previously [42 (link)], using the WinLab software package 4.00 (Perkin–Elmer) and a 1 cm path length Suprasil quartz cuvette (Fisher Scientific, Pittsburgh, PA, USA). The samples were excited at 295 nm to avoid tyrosine fluorescence, and the emission spectra were scanned from 305 to 400 nm at room temperature [43 (link)]. For isothermal denaturation, the effects of urea addition on the secondary structures of SAA and apoA-I in a lipid-bound state were monitored by measuring the α-helicity and tryptophan movement by CD and fluorospectroscopy, as reported elsewhere [25 (link),33 (link)].