Deficient polymerization of human IgM.
It has been suggested that the low disulfide interchange activity in cells producing IgM causes the excretion of immunoglobulin molecules with deficient disulfide cross-linking. IgM material found in the serum formed aggregates which were stabilized largely by noncovalent bonds. Sedimentation coefficients of these aggregates ranged from 11 to 19 S and were similar to sedimentation coefficients calculated for molecules composed of 2, 3, 4 and 5 IgM subunits. A fraction corresponding to a single IgM subunit with a sedimentation coefficient 7.1 S was also present in the serum. The molecular weight of this fraction, determined in mild conditions by Sephadex gel filtration, appeared higher than that predicted for IgMs, reaching the value of 270 000-280 000. The evident increment of molecular weight, compared to a single IgM subunit, was attributed to glycopeptides of sedimentation coefficient 2 S, which form the complex with IgMs molecules. These glycopeptides were also present in aggregates consisting of more than one IgM subunit. The number of IgM subunits participating in aggregates and their molecular weights appeared to depend on the ratio of 2 S glycopeptides to IgM material. With the increase of this ratio the molecular weight of the aggregates lowered and vice versa. Electrical charge and some physico-chemical properties of the aggregates were also significantly affected by the presence of glycopeptides, 2 S glycopeptides were supposed to be the basement membrane related material. Suggestions concerning the interpretation of the phenomenon are presented and discussed.
D000596:Amino Acids / Q000032:analysis; D001665:Binding Sites; D004220:Disulfides / Q000032:analysis; D006801:Humans; D005779:Immunodiffusion; D007122:Immunoelectrophoresis; D007075:Immunoglobulin M / Q000378:metabolism; D046911:Macromolecular Substances; D008970:Molecular Weight; D011485:Protein Binding; D008258:Waldenstrom Macroglobulinemia / Q000276:immunology*
D000596:Amino Acids; D004220:Disulfides; D007075:Immunoglobulin M; D046911:Macromolecular Substances