*4.10. Glutaraldehyde Cross-Linking*

Glutaraldehyde cross-linking was carried out at pH 8.0 (50 mM Tris buffer) in the presence of 0.5 M NaCl at room temperature. Sample volume was 200 μL. Protein concentration was 97 μM (in protomer units). The protocol used was that described previously [60], taking aliquots of a fresh 25% (*w*/*v*) glutaraldehyde solution (Sigma-Aldrich) to yield a final concentration of the cross-linker in the protein solution of 1%. Aliquots of 30 μL were extracted at defined times and the cross-linking reaction was stopped by adding an identical volume of SDS-loading buffer to the aliquot. The extracted samples were run in a 12% SDS-PAGE gel immediately. Experiments were repeated twice.
