Thiol groups and other chemical characteristics of rat monoclonal immunoglobulin A

1. Three aspects of the monoclonal rat IgA IR22 were investigated: its free thiol groups, its hinge structure and its glycopeptides. 2. Exposed thiol groups, 1.5 per IgA dimer, were located in the Fc region, and buried thiol groups, 3.2 per IgA dimer, were located in the Fd region. 3. Rat IgA was cleaved to Fab fragments by pepsin, but, unlike mouse IgA, it was not cleaved at the hinge region by papain. 4. The contents of GlcNAc indicated that there were two N-linked glycopeptides in the Fab region, and one in the Fc or tail regions.