Hetero-oligomerization of wild-type and mutant APP-TM peptides monitored by FRET. Trp-labeled wild-type APP-TM peptides were incubated with equimolar amounts of Edans-labeled V717G APP-TM peptides in the presence of 20 mM SDS. The A/D ratio is plotted as a function of total peptide concentration. Inset: The solid bars represent the A/D ratio of APP-TM homodimers at 50 μM total peptide concentration. The open bars represent the A/D ratio of wild-type and mutant heterodimers at 50 μM total peptide concentration. The gray line indicates the A/D ratio for a mixture of monomeric peptides.