Interactions of pig Fab gamma fragments with protein A from Staphylococcus aureus.

Ninety % of pig serum IgG was bound to protein A-Sepharose. Both individual fractions of the IgG, separated on the basis of their electric charge, were adsorbed on protein A-Sepharose to a similar extent. However, these fractions differed in their elution profile from the protein A-Sepharose when a gradient of increasing molarity of MgCl2 was used. Relative amounts of fractions eluted in higher concentrations of MgCl2 were augmented with the increasing amount of IgG bound to SpA-Sepharose. Not only high proportions of Fc fragments, but also nearly half of Fab fragments reacted with protein A. This latter interaction, confirmed also by affinity electrophoresis, did not have the character of a specific reaction of antibody with antigen.