Fen-B directly targets PS1 and SPP. (A) PAL experiments using mouse brain membranes by Fen-B (10 μM). This labeling was competed by treatment with fenofibrate (200 μM). Note that only PS1 NTF was specifically labeled by Fen-B. Anti-biotin antibody also reacted with a band with ~30 kDa corresponding to PS1 NTF (an asterisk). (B) Fen-B labeling experiment for the DKO cells expressing His-tagged PS1. After PAL, His-tagged PS1 was purified with Ni2+-affinity column and analyzed by immunoblotting. (C) Fen-B also bound endogenous monomeric as well as dimeric SPP (arrows) in CHO cell membranes.