Interactions of pig Fab γ fragments with protein a fromStaphylococcus 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 F_c 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. Parts of this work were presented at the4th European Immunology Meeting, Budapest, 1978. Abstracts p. 152 and at the12th FEBS Meeting, Dresden, 1978, Abstracts No. 727.