immunoglobulin complex, circulating IgM immunoglobulin complex IgM immunoglobulin complex, circulating Note that an IgM immunoglobulin complex has the function of antigen binding if a suitable antigen is available. cellular_component GO:0071754 IgM antibody A polymer of five or six IgM core units each composed of two identical immunoglobulin heavy chains of the IgM isotype and two identical immunoglobulin light chains, held together by disulfide bonds; the individual IgM core units are held together via disulfide bonds with a single J chain polypeptide acting as a bridge between two of the polymeric units. Circulating IgM is present in the extracellular space, in mucosal areas or other tissues, or in the blood or lymph. 2010-03-24T01:44:53Z Ascomycota