Subfragmentation of the Fc fragment of human IgG1 myeloma protein by thermolysin.

Human IgG1 Fc fragment was digested at neutral pH by thermolysin, producing two large subfragments: one comprising the major part of the Fc fragment but devoid of the hinge region; the other comprising the Cgamma3 domain. The former fragment retained the capacity to react with "general" rheumatoid factors whereas the latter did not, indicating that the binding site for "general" rheumatoid factors on the Fc fragment of human IgG1 does not involve the hinge region of the molecule.