Undecagold labelling of glutamine synthetase from E. coli

Glutamine synthetase (GS) from E. coli consists of 12 identical 50 kD subunits arranged in a double hexagon with one six-fold axis of rotational symmetry and six two-fold axes. The divalent cations Mn2+ or Co2+ induce the formation of linear face-to-face aggregates of individual GS molecules, resulting in the formation of long linear arrays, GS/sub n/. This aggregation is retarded and eventually reversed to the native form (GS) as the salt concentration increases. The authors have used an undecagold (11-Au) cluster ion, which induces similar aggregation of native GS, resulting in a wide distribution of ordered linear arrays of GS/sub n/ (where n=2-10, or more). These aggregates show the highly electron dense labels located exclusively at the face-to-face interaction surface. Specimens of the GS/sub n/ aggregates have been studies with the Brookhaven STEM and molecular weight values have been determined with the Brookhaven STEM mass measurement computer system