Which one of the combinations of the following statements is true about antibody structure?
P. Limited proteolysis of rabbit IgG with the enzyme pepsin generates two antigen-binding regions (Fab) and an Fc fragment.
Q. Limited proteolysis of rabbit IgG with the enzyme papain generates a single bivalent antigen-binding region F(ab')₂ and peptide fragments.
R. The Fc fragment of IgG can self-associate and crystallize into a lattice.
S. The F(ab')2 fragment of IgG is composed of both light and heavy chains.