Murine Cell Surface Immunoglobulin: Two Forms of δ-Heavy Chain

The heavy chain of isolated murine cell surface IgD is present in two forms, separable by electrophoresis on SDS-polyacrylamide gradient gels. Both forms of δ-heavy chain are present on the surface of intact spleen cells and have apparent m.w. of approximately 70,000 (δ1) and 68,000 (δ2). Treatment of surface IgD with neuraminidase before isolation results in a single IgD heavy chain band on SDS gels having an apparent m.w. of 65,000, indicating that δ1 and δ2 differ in sialic acid content. Delta2 is removed from the cell surface by papain more readily than δ1, suggesting a possible functional significance for the two forms.