Immunochemical studies on the interaction between staphylococcal protein A and gamma-G globulin.

Reactivity with staphylococcal protein A is a characteristic of IgG-1, -2 and -4 molecules. Human myeloma globulins of these types either precipitate with protein A or are capable of inhibiting such precipitation. In the present study chemical modifications of human myeloma globulins showed distinct effects on the reactivity with protein A. Carbamylation changed a precipitin reaction to one of inhibition. Acetylation rendered myeloma globulins completely non-reactive with protein A. Quantitative precipitin curves for the reaction between normal human γG or various myeloma globulins and staphylococcal protein A revealed marked quantitative differences with varying amounts of soluble complexes formed. Analytical ultracentrifugation of γG preparations with and without protein A revealed similar differences. No intermediate sized complexes were detected. Our results confirm a previous hypothesis that precipitation in this system is a secondary reaction after the primary combination between protein A and the Fc site on human γG globulin. Ultracentrifugational data also indicated that protein A may be univalent, structurally or functionally, in its reaction with γG.