Three New Fragments, F(ab)₂, F(c)₂, and Fab/c, Obtained by Papain Proteolysis of Normal Human IgG.

Three new fragments, each with a molecular weight of about 100,000, were isolated after papain proteolysis of normal monomer human IgG. The fragments isolated were as follows: F(c) 2 fragment with Fc determinants only, Fab/c fragment with both Fc and Fab determinants, and F(ab′) fragment with only Fab determinants. The F(c) 2 fragment appeared to be a dimer of Fc stabilized by disulphide bonds, whilst the F(ab) 2 fragment consisted of Fab subunits mainly held together by non‐covalent forces. The Fab/c fragment is probably a single Fab fragment and the Fc fragment held together by an unbroken heavy chain.