A BAK-6H on liposomes was activated (+cBID, bottom) or not (Control, top) with cBID for 60 mins prior to deuteration for 10 s, 60 s, 600 s, or 3600 s. Incorporation of deuterium was assessed by mass spectrometry and is expressed relative to a non-deuterated sample and a theoretical maximum. HDX-MS reveals that following activation with cBID, maximal deuteration of the BAK N-terminus (up to amino acid 58) occurred within 10 secs. 