Nonantibody binding of serum proteins to 5S anti-Rh fragments produced by chymotrypsin.

Chymotrypsin hydrolysis of the IgG anti-Rh antibodies Ri results in both bivalent and univalent antibody fragments. The bivalent fragments coated on Rh-positive erythrocytes are agglutinable by albumin and other serum proteins in 3% polyethylene glycol. The bivalent structure of the 5S fragment is essential for expression of this site since 5S fragments produced by trypsin and pepsin are also agglutinable, while univalent fragments produced by papain and subtilisin are not. The agglutination by albumin of the 5S fragments is not caused by residual enzyme. The reaction appears to be irreversible in that once albumin has reacted with the 5S fragment, either in the fluid phase or at the cell surface, fresh addition of albumin and PEG will not result in agglutination. The nonantibody reaction of albumin and the other serum proteins with these 5S IgG fragments is believed to be caused by hydrophobic bonding involving the intrachain disulfide in the 5S fragment and hydrophobic areas of other proteins.