A new antigen common to the rat nervous and immune systems: II. Molecular characterization.

G5-IgG is a monoclonal antibody that binds specifically to some cells and tissues of the adult rat nervous and immune systems. The molecular nature of the G5 antigen from adult rat brain is described in this paper. G5 antigen in adult rat brain membrane fractions was trypsin-sensitive and heat-labile but not chloroform/methanol-soluble. It was solubilized by the nonionic detergent NP40 but not by 3 M KCl. Detergent-soluble rat brain particulate protein inhibited G5-IgG binding to glutaraldehyde-fixed rat brain particulate protein. Inhibitory activity could be removed by prior incubation with concanavalin-A agarose beads. Immunoprecipitates of enzymatically iodinated, detergent-solubilized brain particulate protein gave a single band on polyacrylamide gels of apparent molecular weight 95,000--105,000 daltons. A band of identical molecular weight was visualized in gels of unlabeled immune precipitates by 125I-concanavalin A. These results strongly suggest that G5 is an integral membrane glycoprotein in adult rat brain.