Studies of carcino‐fetal proteins. II. Biochemical comparison of α‐fetoprotein from human fetuses and patients with hepatocellular cancer

Abstract α‐fetoprotein from human fetuses and patients with a hepatocelhlar cancer was isolated and characterized. In accordance with earlier reports, the two proteins had similar electrophoretic mobilities and gave a reaction of immunological identity. They had very similar amino acid compositions. Each was composed of a single polypeptide chain with a molecular weight of 70,000. Protein from both sources had about 4 % carbohydrate with 2 moles of sialic acid per mole of protein. Tryptic digests of the isolated fetal and cancer α‐fetoproteins were compared by peptic mapping. About 30 peptides were seen and the patterns given by the two proteins were indistinguishable. Thus both fetal and cancerous liver cells produce α‐fetoproteins which are structurally indistinguishable and probably identical.