Fluorescence anisotropy (FA) competition assays were used to evaluate the inhibitory potencies. NOXA-B gave an inhibitory response in line with previous reports (IC50 = 0.4 ± 0.1 µM, Fig. ). Amongst BH3 ligands, NOXA-B preferentially binds to MCL-1. BCL-xL is another highly α-helical anti-apoptotic protein that interacts with different selectivity towards pro-apoptotic modulators. Both MCL-1 and BCL-xL recognize BID, though BCL-xL does not recognize NOXA-B. FA competition assays reflected this specificity: the NOXA-B peptide showed no inhibitory response in the corresponding BCL-xL FA competition assay (Fig. ).