Relationship between epitope density and immunoprecipitation of multivalent antigens by bivalent antibody: immunoprecipitation of adenylylated glutamine synthetase by anti-AMP antibodies

Separation of glutamine synthetase species with different states of adenylylation by chromatography on monoclonal anti-AMP antibody affinity columns

Glutamine synthetase [GS; L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2] from Escherichia coli is composed of 12 identical subunits arranged in two superimposed hexagonal arrays. Therefore, partially adenylylated GS is a mixture of hybrid molecules containing different numbers (from 0 to 12) and distributions of adenylylated subunits. In an effort to separate these GS species into uniquely adenylylated molecular species, immunoadsorbants were prepared by covalent attachment of monoclonal antibodies, 72-76-1 (IgG2a and 37-2-1 (IgM), to Affi-Gel 10. The bound GS was eluted with AMP gradients. The results indicate that the IgG column and IgM column yield significantly different elution profiles; the column prepared with the IgG monoclonal antibody better resolves GS containing fewer than 3 adenylylated subunits per dodecamer, whereas the column prepared from the IgM monoclonal antibody better resolves the GS containing higher numbers (from 4 to 12) of adenylylated subunits. In addition, the results indicate that both the distribution and the number of adenylylated subunits are important factors in this separation.