Immune response region-associated antigens of the mouse. Biochemical properties of detergent and papain solubilized molecules

Immune response region-associated (Ia) antigens and classical H-2 antigens are glycoproteins which differ in their molecular weight and tissue distribution. Ia and H-2 molecules also show differences in overall charge, apparent isoelectric point and susceptibility to proteolytic degradation, acid treatment and exposure to 56°C. In the present paper, Ia.11^d antigens were shown to have a molecular weight of about 35 000 after solubilization with non- ionic detergents. Purified Ia^d antigens, solubilized by controlled papain digestion, display a molecular weight of about 26 000 after final purification by indirect immune coprecipitation. This figure corresponds to the molecular weight of a highly purified H-2 polypeptide fragment obtained after papain solubilization. The remarkable size similarity of proteolytic fragments from Ia and H-2 antigens could suggest that these genetically and functionally related molecules possess some structural features in common.