Mechanism of IgM polymerization.
The stoichiometry of J chain in pentamer IgM has been determined by measuring the radiolabeled thiols in the constituent chains after complete reduction and alkylation of the polymer. One mole of J was found to be disulfide bonded to 1 mol of pentamer. The linkage of J chain in IgM has been determined by correlating the J disulfides cleaved with the subunits released after limited reduction and alkylation of the polymer. The analyses showed that: (a) Significant amounts of monomers, as well as small quantities of dimers, trimers, and tetramers, were generated by the reducing conditions employed. (b) The number of J disulfide bonds broken did not correspond to the extent of depolymerization. (c) No J disulfides were cleaved in the J-containing dimer products of the limited reduction. These data demonstrated that the J chain is located as a disulfide clasp between two of the IgM monomer subunits. From the observed linkage, the assembly of IgM is postulated to proceed by a series of sequential disulfide exchanges beginning with the formation of the J-containing dimer.
D000478:Alkylation; D002250:Carbon Radioisotopes; D055598:Chemical Phenomena; D002621:Chemistry; D003545:Cysteine / Q000032:analysis; D003553:Cystine / Q000032:analysis; D004229:Dithiothreitol; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007144:Immunoglobulin J-Chains; D007075:Immunoglobulin M / Q000032:analysis*; D007461:Iodoacetates; D010084:Oxidation-Reduction; D011108:Polymers; D014316:Tritium
D002250:Carbon Radioisotopes; D007144:Immunoglobulin J-Chains; D007075:Immunoglobulin M; D007461:Iodoacetates; D011108:Polymers; D014316:Tritium; D003553:Cystine; D003545:Cysteine; D004229:Dithiothreitol