PUMA BH3, a peptide that includes the BH3 domain from the p53-upregulated modulator of apoptosis (PUMA) and activates the pro-apoptotic protein Bak, demonstrates binding affinity to Bak with dissociation constants (Kds) of 290 nM in HEPES buffer and 26 nM in CHAPS buffer. This interaction with Bak induces its homo-oligomerization and facilitates Bak-mediated membrane permeabilization.