APP-TM peptides oligomerize within phospolipid bilayers. Different forms of fluorescent donor (Trp) and acceptor (Edans) labeled APP-TM peptides were incorporated in DOPG phospholipid vesicles. Purified peptide-incorporated vesicle fractions were subjected to fluorescence measurements. Typical donor quenching and acceptor sensitization was observed and is indicative of FRET. The fluorescence spectra of donor-labeled APP-TM wild-type peptide (□), acceptor-labeled APP-TM wild-type peptide (○), and a mixed sample (●) are shown. Note: arrows show donor quenching and acceptor sensitization and indicate that the peptides oligomerize in phospholipid bilayers. Inset: FRET decreases with increasing concentration of unlabeled peptide in phospholipids bilayers. Equimolar mixtures of donor- and acceptor-labeled APP-TM peptides were mixed with increasing concentrations of unlabeled peptide. Total peptide concentration was held constant at 100 μM. The unlabeled peptides act as competitors and reduce the likelihood of forming dimers containing both donor- and acceptor-labeled peptides, which results in a decrease in FRET and A/D ratio.