Anti-API-5 antibodies enable researchers to detect and measure the API-5 antigen in biological samples. This target is a reported synonym of the API5 gene, which encodes apoptosis inhibitor 5. This protein is known to function in the apoptotic pathway, among other biological roles. The human version of API-5 has a canonical amino acid length of 524 residues and a protein mass of 59 kilodaltons, although 6 isoforms have been identified. It is reported to be localized in the nucleus and cytoplasm of cells and widely expressed in many tissue types. API-5 is a member of the API5 protein family.