A comparison of the proteolytic fragmentation of immunoglobulin M from several different mammalian species.

1. IgM from six different mammalian species was fragmented with three different proteases. 2. Differences occurred in the proteolysis of the same domain of different species and different domains of the same species. 3. The inter-chain disulphide bridge in the C mu2 domain moderated the nature of the fragments. 4. No well defined polymeric fragment lacking the C mu2 disulphide bridge was obtained. 5. Only in a few cases did fragmentation proceed in regular steps and produce a well defined series of partially fragmented molecules.