Bak is a homolog of apoptosis inhibitor Bcl-2. Bak is a member of the Bcl-2 family of proteins and contains Bcl-2 homology region (BH-) 1, 2 and 3. Unlike Bcl-2, Bak promotes cell death and counteracts the anti-apoptotic effect of Bcl-2. The immunoaffinity purified antibody detects a 30 kDa band, corresponding to the expected molecular weight of Bak on SDS-PAGE immunoblots.