title: Further characterization of the membrane anchor found on the tissue-specific class I molecule Qa2.
abstract: Previous studies have determined that various Qa2 serologic determinants can be removed from the surface of spleen cells by treatment with a phospholipase C. Our studies have determined that the class I molecule Qa2, expressed on the surface of spleen cells and activated T cells, behaves as an integral membrane protein based on its ability to associate with detergent micelles. Studies utilizing two purified phospholipase C have revealed that although most (90 to 95%) of the Qa2 molecules expressed on the surface of resting spleen cells are released as intact 40-kDa polypeptides associated with beta 2-microglobulin, activated T cells contain a major cell subpopulation expressing lipase-resistant Qa2 molecules. Flow cytometric analysis revealed that L3T4+-activated T cells expressed lipase-sensitive Qa2 molecules, whereas Lyt-2+ cells express lipase-resistant forms of the Qa2 molecule. The relationship between the secreted form of the Qa2 molecule and the lipase-generated soluble Qa2 molecule was investigated. Based on SDS-PAGE analysis, the secreted Qa2 molecules has a Mr of 39 kDa whereas the cell surface form released from either resting spleen or activated T cells by phosphatidylinositol-specific phospholipase C has a Mr of approximately equal to 40 kDa. Furthermore, the secreted Qa2 molecule lacks an epitope, cross-reacting determinant, often present on lipase-solubilized cell surface molecules. Thus, based on serologic and biochemical criteria, the soluble Qa2 molecules generated by an exogenous phospholipase C and the secreted Qa2 molecule are structurally distinct.
mesh_terms: D000818:Animals; D000939:Epitopes / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D006649:Histocompatibility Antigens / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D008049:Lipase / Q000494:pharmacology; D008051:Lipid Bilayers; D008213:Lymphocyte Activation; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D051379:Mice; D008810:Mice, Inbred C57BL; D010716:Phosphatidylinositols / Q000502:physiology; D013154:Spleen / Q000166:cytology* / Q000276:immunology; D013601:T-Lymphocytes / Q000145:classification / Q000201:enzymology / Q000276:immunology*; D014346:Trypanosoma brucei brucei; D010738:Type C Phospholipases / Q000502:physiology; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000235:genetics
chemical_list: D000939:Epitopes; D006649:Histocompatibility Antigens; D008051:Lipid Bilayers; D008562:Membrane Glycoproteins; D010716:Phosphatidylinositols; D014643:Variant Surface Glycoproteins, Trypanosoma; D008049:Lipase; D010738:Type C Phospholipases