Tryptic cleavage of rat IgG: a comparative study between subclasses.

Monoclonal rat IgG belonging to the 4 rat IgG subclasses, and some IgG subclasses isolated from normal rat serum were subjected to enzymatic degradation with trypsin. Differences in the products of tryptic digestion were observed according to the IgG subclass. IgG2b and IgG2c were degraded mainly into Fab and Fc fragments. IgG1 and IgG2a appeared resistant to such cleavage. However, tryptic digestion of the latter two produced two fragments separated only in dissociating media. Results of the studies suggest that one of the fragments (mol. wt. 13,000) probably consists of most of the variable domain of the gamma heavy chain, while the second (mol. wt. 120,000) consists of the IgG deleted of the VH regions.