Small-angle X-ray studies of a human immunoglobulin M.

The conformation of a Waldenström immunoglobulin M (IgM) with antibody-like activity for X-ray contrast media, based on 3-amino-2,4,6-triiodobenzoic acid, was studied by small-angle X-ray scattering. The radius of gyration was determined as 12.1 nm, the maximum distance 35 nm, the volume 1900 nm3. A flat star-shaped model was found to be equivalent in scattering. Aggregation of IgM molecules seems to take place as side-by-side combinations of single molecules, manifesting itself as a relatively large increase of the radius of gyration and unchanged thickness of the flat aggregates.