AP endonucleases are enzymes that play a crucial role in the DNA repair process. They specifically recognize and cleave the phosphodiester bond at apurinic/apyrimidinic (AP) sites, which are locations in the DNA where a base has been lost. This action creates a break in the DNA strand, allowing other repair mechanisms to take over and restore the integrity of the genetic material. These enzymes are essential for maintaining genomic stability and preventing mutations. In humans, APE1 is the most studied AP endonuclease, and it is involved in the base excision repair pathway. Proper functioning of AP endonucleases is vital for cellular health and longevity.