title: Immunoglobulin M biosynthesis. Production of intermediates and excess of light-chain in mouse myeloma MOPC 104E.
abstract: Immunoglobulin M (IgM) biosynthesis was studied with mouse plasma-cell tumour MOPC 104E as a model system. Cell suspensions prepared from solid tumours were incubated in vitro with [(3)H]leucine; the radioactivity incorporated into intracellular and secreted proteins was analysed by sucrose-density-gradient centrifugation and polyacrylamide-gel electrophoresis. The tumour secretes IgM and light chains. ;Pulse-chase' experiments indicated average secretion times of 1.5h for light chain and 2.5h for IgM. The order of disulphide-bond assembly within the cell was shown to be heavy chain+light chain --> heavy chain-light chain intermediate --> IgMs. The 7S subunit (IgMs) was polymerized into IgM just before or at the time of secretion. Measurements of heavy-chain/light-chain radioactivity ratios in intracellular HL and IgMs and secreted IgM demonstrated the existence of a light-chain pool participating in IgM biosynthesis. The size of the light-chain pool, together with analysis of clones isolated in vivo, suggested that the tumour contains cells in which light-chain synthesis is in excess of heavy-chain production.
mesh_terms: D000818:Animals; D002499:Centrifugation, Density Gradient; D002999:Clone Cells / Q000378:metabolism; D004220:Disulfides / Q000096:biosynthesis; D004589:Electrophoresis, Disc; D007074:Immunoglobulin G / Q000378:metabolism; D007136:Immunoglobulins / Q000096:biosynthesis* / Q000378:metabolism; D066298:In Vitro Techniques; D007930:Leucine / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D009101:Multiple Myeloma / Q000378:metabolism*; D009374:Neoplasms, Experimental / Q000378:metabolism; D013395:Sucrose; D014316:Tritium
chemical_list: D004220:Disulfides; D007074:Immunoglobulin G; D007136:Immunoglobulins; D014316:Tritium; D013395:Sucrose; D007930:Leucine