Enzymatic cleavage products of the alpha subunit of the receptor for immunoglobulin E.
The high-affinity membrane receptor for immunoglobulin E on mast cells and on a tumor analogue, rat basophilic leukemia cells, consists of two polypeptide chains: an alpha chain of Mr congruent to 50,000 and a beta chain of Mr congruent to 30,000. In this study we reacted alpha chains purified from tumor cells with proteolytic and glycolytic enzymes and compared the products by using differential labeling procedures. A variety of proteolytic enzymes cleave the chain into two similar-sized fragments, alpha 1 and alpha 2. The alpha 1 fragment behaves as if it were slightly larger on electrophoresis through polyacrylamide gels and is rich in carbohydrate as determined by incorporation of [14C]glucosamine. Less incorporation is observed into alpha 2 but it, like alpha 1, binds to concanavalin A. Labeling of the surface proteins on intact cells by lactoperoxidase-catalyzed iodination leads to preferential, perhaps exclusive, labeling of the alpha 2 fragment. The relative proportion of incorporated 3H-labeled amino acids and radioactive Bolton--Hunter reagent suggests that the polypeptide portions of alpha 1 and alpha 2 are similar in size. From these and other data we propose that the alpha chain may be U-shaped. Results from endoglycosidase digestions show that the receptor as isolated is heterogeneous because of variable glycosylation.
D000818:Animals; D002918:Chymotrypsin; D006026:Glycoside Hydrolases; D007073:Immunoglobulin E / Q000276:immunology*; D007942:Leukemia, Experimental / Q000276:immunology*; D046911:Macromolecular Substances; D008407:Mast Cells / Q000276:immunology; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D011487:Protein Conformation; D051381:Rats; D017455:Receptors, IgE; D011971:Receptors, Immunologic; D014357:Trypsin
D046911:Macromolecular Substances; D010446:Peptide Fragments; D017455:Receptors, IgE; D011971:Receptors, Immunologic; D007073:Immunoglobulin E; D006026:Glycoside Hydrolases; D002918:Chymotrypsin; D014357:Trypsin