The influence of enzymatic cleavage and chemical modification of human and rabbit IgG on their reactivity with staphylococcal protein A.

Proteolytic cleavage fragments from rabbit IgG have been isolated and characterized in an attempt to locate the sites involved in the reactivity with Staphylococcal protein A. The plasmin cleavage product Facb together with the pepsin cleavage products F(ab')2 and pFc' failed to react in contrast to the papain Fc fragment. These data, together with data from unfractionated plasmin digests, in which the Facb fragment remains associated with the plasmin pFc' fragment, indicate that inter-domain interactions are important in the maintenance of this activity. beta2-microglobulin was also shown to be unreactive with protein A. Chemical modification studies employing flurescamine, tetranitromethane and potassium cyanate indicate that lysine and tyrosine residues are not involved in the reactivity of human and rabbit IgG with protein A.