Isolation of enzymatically derived fragments of porcine IgG and an examination of their reactivity against staphylococcal protein A.

Papain digestion of porcine IgG in the absence of cysteine resulted in a rather poor yield of fragments (less than 5 per cent). In the presence of cysteine, 70 to 80 per cent of the IgG was degradated in 4 h. Fragments with molecular weight of about 100,000 and 50,000 were separated by gel filtration. The minor fraction (mol. wt. 100,000) most probably consisted of F(c)2 fragments. Fab/c fragments with both Fc and Fab determinants, and also probably some F(ab)2-like fragments. The F(c)2 fragments appeared to be a dimer of Fc stabilized by disulphide bonds. The second main fraction (mol. wt. 50,000) contained Fc and Fab fragments. Mild reduction of the Fc fragments resulted in Fc subfragments of different sizes, thus indicating that papain cleavages had occurred on different spots in the Fc chain. Non-reduced Fc fragments therefore seem to consist of several Fc subfragments stabilized by disulphide bonds. The protein A reactivity of the isolated Fc fragments were rather low compared to the reactivity of intact IgG, respectively 5--15 and 90 per cent. In addition, protein A reactive Fab fragments were isolated from normal porcine IgG.