Amyloid P component, serum (SAP), also known as PTX2 or APCS, is the identical serum form of amyloid P component (AP), a 25kD pentameric protein first identified as the pentagonal constituent of in vivo pathological deposits called "amyloid". It belongs to the pentraxins family, characterised by calcium dependent ligand binding and distinctive flattened beta-jellyroll structure similar to that of the legume lectins. This gene is mapped to 1q23.2. The binding of the encoded protein to proteins in the pathological amyloid cross-beta fold suggests its possible role as a chaperone. This protein is also thought to control the degradation of chromatin. It has been demonstrated that this protein binds to apoptotic cells at an early stage, which raises the possibility that it is involved in dealing with apoptotic cells in vivo.