Characteristics of a cell surface antigen defined by an anti-human osteogenic sarcoma monoclonal antibody

The expression of a cell surface antigen defined by an anti-human osteogenic sarcoma monoclonal antibody was analysed by flow cytofluorometry using fluorescein-labelled antibody. Quantitative absorption tests established that the antigen was associated with plasma membranes, whereas cytosol, cellular lipids and nuclei were largely devoid of activity. Single-phase aqueous butanol solutions at non-cytolytic concentrations failed to solubilize the antigen, although treatment of cells with papain virtually abolished antigenic activity. The antigen was shown to be solubilized by the non-ionic detergent Nonidet P-40, and following lactoperoxidase-catalysed radioiodination of viable cells, extraction with detergent, immunoprecipitation of antigen with monoclonal antibody and Sepharose-Protein A, the molecular weight of antigen was determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The findings indicate that this human osteogenic sarcoma antigen is a monomeric integral membrane protein with an apparent molecular weight of 72,000, which is predominantly expressed at the external face of the tumour cell plasma membrane.