TUNEL In Situ Apoptosis Kit (HRP-DAB Method)

When cells undergo apoptosis, endonuclease enzymes are activated to cleave the genomic DNA between nucleosomes. When genomic DNA is cleaved, the exposed 3′-OH can be added with a biotinylated dUTP (Biotin-dUTP) due to the catalysis of Terminal Deoxynucleotidyl Transferase (TdT), followed by the binding of horseradish Peroxidase-labeled Streptavidin (Streptavidin-HRP). Thereafter, through the HRP catalysis, the apoptotic cells are marked by DAB, which can be detected by ordinary microscopy. This is the principle of TUNEL (TdT-mediated dUTP Nick-End Labeling) for detecting apoptosis.