Proteolysis of rabbit immunoglobulin M by papain

1. Digestion of rabbit immunoglobulin M (IgM) by papain for 5h, in the absence of reducing agent, gives Fabmu and Fc(5)mu fragments in high yield. Shorter periods give fragment Fc(5)mu with one or more Fabmu fragments still attached. 2. Reducing agent in the absence of a denaturant cleaves rabbit IgM into half-subunits, each containing one mu chain and one light chain. Digestion by papain in the presence of such a reducing agent destroys the Fcmu domains.