Murine cell surface immunoglobulin: two forms of delta-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 delta-heavy chain are present on the surface of intact spleen cells and have apparent m.w. of approximately 70,000 (delta1) and 68,000 (delta2). 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 delta 1 and delta 2 differ in sialic acid content. Delta 2 is removed from the cell surface by papain more readily than delta 1, suggesting a possible functional significance for the two forms.