Development and application of an efficient procedure for converting mouse IgM into small, active fragments.

A simple method is described for generating active molecules with molecular weights between 110 and 230 kilodaltons from mouse immunoglobulin M. The majority of these molecules have a 1 : 1 ratio of intact heavy and light chains. Approximately 70% of the specific IgM protein will still bind antigen after digestion with only a small decrease in binding affinity. Both anti-kappa and anti-mu chain specific antisera recognize these molecules. These low molecular weight molecules are much more efficient in immunocytochemistry and have localized antigens that could not be detected with undigested IgM.