Purification and characterization of human liver specific F antigen

This paper reports the properties of purified human F antigen (liver-specific antigen). Homogenates of liver in 0-25 M sucrose were centrifuged at 105,000 g. The supernatants were chromatographed on Sepharose 6-B and four major peaks were separated. The third peak proved to be predominantly F antigen. This fraction was subsequently subjected to DEAE-cellulose column chromatography and F antigen was eluted at a concentration less than 0-2 M NaCl in 0-01 M sodium phosphate buffer (pH 7-2). Finally, purified F antigen was obtained after preparative isoelectric focusing. Purified human F antigen was found to have a mol. wt between 40,000 and 80,000, a pI of 6-5-6-7 and a density of 1-26. It is a protein antigen and contains no detectable carbohydrate or lipid. No differences were found in purified F-antigen preparations from several species when tested by sodium dodecyl sulphate (SDS) disc gel electrophoresis. Immunofluorescent studies showed that F antigen was homogeneously distributed in the cytoplasm of liver cells but was not present on the cell surface. Immunization of guinea-pigs with purified human liver-specific protein did not induce antibody to the F antigenic determinant defined by mouse anti-F antiserum. It did, however, induce antibodies to two human liver antigens. One of these seems to be a human-specific determinant on the F antigen molecule and the other appears to be a separate molecule which is similar in molecular weight and electrophoretic mobility to the F-antigen molecule.