Abstract
Further characterization of three polypeptide antigens present in Novikoff ascites hepatoma (molecular weights 39,000, 49,000, and 56,000--p39, p49, and p56, respectively), has established the identity of these proteins as cytokeratins. Two-dimensional gel electrophoresis revealed that each of the three proteins exists in several isoelectric forms, all characteristic of the keratins. The antigens p39, and p56 had amino acid compositions compatible with this family of proteins, and immunofluorescence microscopy localized the antigens on elaborate filament arrays indicative of the cytokeratins. Antibodies monospecific for the p39 antigen, purified by using affinity chromatography, were used to demonstrate that protein p39 was specific for Novikoff hepatoma cells. These results suggest that the cytokeratins contain cell-specific that can be useful as markers for differentiation and neoplasia.