Detection of the glycoprotein antigen for antibodies V.1A7, V.5C7, and V.7C7 by immunoprecipitation. Mouse bEND.3 cells were surface biotinylated and detergent extracts were incubated either with protein A Sepharose loaded with rabbit antirat IgG and the MoAbs V.1A7, V.5C7, or V.7C7 or a control antibody, as indicated. Specifically bound proteins were eluted with SDS-PAGE loading buffer, electrophoresed on an 8% polyacrylamide gel under reducing conditions, and transferred to nitrocellulose. Filters were incubated with peroxidase-conjugated streptavidin and analyzed by enhanced chemiluminescence.