Treatment of Escherichia coli glutamine synthetase (GS) with various cross-linking reagents led to the generation of at least 10 different molecular weight species when the treated enzyme is subjected to sodium dodenyl sulfate disc gel chromatography. From measurements of the rapid quenching of tryptophan fluorescence associated with the binding of anti-AMP-antibodies with adenylylated GS subunits, it was found that the primary binding of antibodies to adenylylated subunits is independent of the fraction of adenylylated subunits per molecule. However, measurements of the slow change in light scattering which follows the primary interaction show that lattice formation is dependent on both the number of adenylylated subunits per molecule and on the total concentration of adenylylated subunits. Dissociation and reassociation of mixtures of unadenylylated and fully adenylylated GS molecules leads to hybrid molecular forms which exhibit immunoprecipitation patterns that are similar to those of partially adenylylated native GS preparations.