Density differences between membrane and secreted immunoglobins of murine splenocytes

Area of Science:

• Immunology
• Biochemistry
• Molecular Biology

Background:

• Immunoglobulins (Igs) are crucial proteins in the immune system.
• Understanding their biophysical properties, like buoyant density, is key to characterizing different forms.
• Variations in Ig structure, including glycosylation, can affect their properties.

Purpose of the Study:

• To determine the buoyant densities of various mouse immunoglobulins.
• To investigate the influence of carbohydrate content and detergent on Ig buoyant densities.
• To differentiate between membrane-bound and secreted forms of immunoglobulins.

Main Methods:

• Isopycnic centrifugation in cesium chloride gradients was employed.
• Beta-galactosidase served as a marker for density calibration.
• Nonidet P-40, a nonionic detergent, was used to lyse cells and solubilize membrane proteins.

Main Results:

• Buoyant densities of IgG, IgA, and secreted IgM correlated with their known carbohydrate content.
• Intracellular IgM exhibited a buoyant density suggesting approximately 6% carbohydrate.
• Membrane IgM was less dense than intracellular or secreted IgM in detergent.
• IgD-like membrane molecules were denser than membrane IgM.

Conclusions:

• Buoyant density is a reliable indicator of carbohydrate content in mouse immunoglobulins.
• Membrane-bound IgM and IgD-like molecules possess distinct biophysical properties compared to secreted forms.
• Detergent affects the buoyant density of membrane-associated immunoglobulins.