Identification and characterization of the CO17-1A carcinoma-associated antigen

The cell surface antigen defined by monoclonal antibody CO17-1A is sensitive to proteinase K but not to neuraminidase digestion. Immunoprecipitation of two polypeptide chains of 30 and 40 kDa using large amounts of CO17-1A antibody confirmed that the CO17-1A antigen is a protein. The requirement for large quantities of CO17-1A antibody may relate to the binding properties of this antibody, as bivalent but not monovalent (Fab) forms of the antibody bind effectively to carcinoma cells. The 30 kDa form of the CO17-1A antigen was purified by immunoaffinity chromatography using GA733, another monoclonal antibody that recognizes the CO17-1A antigen. Treatment of purified antigen with endoglycosidase F revealed a 25 kDa and a 28 kDa species, demonstrating that the antigen has at least two N-linked oligosaccharide chains. Protease treatment of the purified antigen revealed a 26 kDa protease-resistant polypeptide.