When a Mixture of Different IgG Antibody Proteins Are Treated

Multiple Choice

When a mixture of different IgG antibody proteins are treated with the enzyme papain, each antibody is cleaved into three roughly equal size fragments. From each original antibody, two of the three fragments are identical to each other, and represent the 'arms' of the antibody 'Y'. These fragments are known as Fab fragments. The third fragment is known as the Fc region, because this fragment will crystallize when purified. The reason a mixture of Fc fragments will crystallize is because:

A) It is the only part of the antibody protein that can easily be purified at the high concentrations needed for crystallization.
B) It has no disulfide bonds holding the domains together, as disulfide bonds will inhibit crystallization.
C) It is the only fragment of the antibody that still has disulfide bonds, so it remains intact during the crystallization process.
D) The Fc fragments of IgG are much more water soluble than the Fab fragments.
E) All Fc fragments generated from a mixture of IgG molecules have the identical amino acid sequence.