Active caspase-3 is a protein encoded by the CASP3 gene which is approximately 31,6 kDa. Active caspase-3 is localised to the cytoplasm. It is involved in the TNFR1 pathway, apoptosis modulation and signaling and respiratory electron transport. This protein falls under the cysteineaspartic acid protease family. It is a sequential activator of caspases and plays a central role in the execution-phase of cell apoptosis. Caspases exist as inactive proenzymes which undergo proteolytic processing at conserved aspartic residues to produce two subunits, large and small, that dimerize to form the active enzyme. Active caspase-3 is highly expressed in lung, spleen, heart, liver and kidney. Mutations in the CASP3 gene may result in bladder urothelial carcinoma and primary effusion lymphoma. Active Caspase 3 was affinity-purified from mouse ascites by affinity-chromatography using epitope-specific immunogen. This antibody detects endogenous active caspase-3 protein.