Papain hydrolysis products in four M-IgG subclasses.

Four different classes of monoclonal IgG were submitted to papain digestion activated by cysteine. After digestion of subclasses G-1, 3 and 4 about 80% of the initial amount of IgG is converted to fragments Fab and Fc (less in subclass IgG2). In the initial time of digestion subfragments: Fc', Facb-like and nonidentified product of digestion (fraction IV) are also obtained. Additional products (besides Fab and Fc) corresponded to 11-17% of the initial amount of IgG. In contrast to fragments Fab and Fc the amounts of additional fragments did not increase during the time of digestion and the amount of fragment Facb-like in G-1 and G-3 subclasses even decreased at the end of hydrolysis. It is possible that fragment Facb-like is an intermediate product of immunoglobulin digestion. IgG2 was resistant in 60% to 18 h--hydrolysis performed under conditions described. Only 20% of IgG2 was digested to Fab and Fc fragments and 20% to other products of digestion.