Fig. 1.

Accumulation of a single-cleaved proteolytic product of IgG in vitro and its detection in vivo. (A) Capillary gel electrophoresis depiction of partial digestions of mAb4 with human and bacterial proteases under denaturing, nonreducing conditions. Specific enzymes and digestion times are indicated above the lanes. The right hand lane contains a mixture of purified standards of mAb4 and its proteolytic fragments. The single-cleaved intermediate is denoted as scIgG, and the Fc monomer released under denaturing conditions is denoted Fc(m). (B) Schematic model of a human IgG1 with the position of the lower hinge cleavage indicated. Single-cleaved IgG is intact under native (nondenaturing) conditions, and the Fc monomer dissociates under denaturing conditions. (C) Detection of IgG components in protein A-purified synovial fluid (SF) from three patients with rheumatoid arthritis and from three human breast tumor extracts. Immunoblotting was performed with an anti-Fc gamma domain antibody following SDS-PAGE under denaturing, nonreducing conditions.