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. Δ₂ is removed from the cell surface by papain more readily than δ₁, suggesting a possible functional significance for the two forms.