Molecular mechanisms of the immunologic activation of a defectiveescherichia coli β-d-galactosidase—I

Antibodies toEscherichia coli β-d-galactosidase form distinct sub-populations which segregate independently during the response: thus precipitating and activating molecules are distinguished. The latter molecules react with a defective mutant enzyme. AMEF, and activate its catalytic site, which then interacts with the subsrate. As a step toward elucidating the mechanism of AMEF activation, some properties of the relevant anti-enzyme antibodies were determined. Antibody class and valence do not affect activation: equal activation was obtained with IgM, IgG and Fab molecules over a 100-fold range of AMEF concentrations. Precipitating antibodies do not influence activation or compete with activating molecules. Most or all antienzyme antibodies produced by 15 rabbits were IgG. Three rabbits also produced small amounts of IgM antibodies, but only within 2 weeks after immunization. Non-activating IgM molecules from immune sera did not compete with activating IgG molecules, whether or not these IgM molecules were able to bind the enzyme, as demonstrated by precipitation or by coprecipitation with anti-μ-chain antisera.