Apoptosis activator 2 is a cell-permeable apoptosis activator that promotes the cytochrome c-dependent oligomerization of Apaf-1 into the mature apoptosome. Increases procaspase-9 processing and subsequent caspase-3 activation. Induces apoptosis in tumor cells (IC50 = 4 - 9 μM for leukemia cells) with weak or no effect on normal cell lines or those defective/deficient in Apaf-1, caspase-9 or caspase-3 activity (IC₅₀ > 40 μM).