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. (Gene Ontology, GO_0071754)
1 proteins localized to the igm immunoglobulin complex, circulating cellular component from the curated GO Cellular Component Annotations 2015 dataset.
