Bax is a Bcl-2 family pro-apoptotic protein. Bax promotes cell death by forming homodimers, which can be blocked by forming heterodimers with Bcl-2 or Bcl-XL. Bax has three different isoforms, which are Bax-α, β, and g. The 21 kDa Bax-α is the most common form in most of the cells and tissues.