Derivative crystals of hexagonal HEWL with TPT and TaB. A stereo representation of a section of the solvent-flattened experimental electron-density map is shown calculated from SAD phases (blue mesh, contoured at 1σ) together with the anomalous difference Fourier map of tungsten and tantalum (orange mesh contoured at 5σ) for (a) HEWL–TPT (1.9 Å resolution) and (b) HEWL–TaB (1.9 Å resolution), respectively. HEWL is shown in stick representation; blue and purple C atoms mark two symmetry-related molecules. (a) TPT oriented by MR is shown in stick representation with light blue W and red O atoms. Owing to degradation, only 11 W atoms reside within the heavy-atom cluster, whereas additional peaks were found in the anomalous Fourier map. Black and grey arrowheads mark the positions of the missing and additional W atoms, respectively. (b) The TaB cluster at binding site 1 was found by MR at 1.8 Å resolution and is shown in stick representation. The twofold crystallographic symmetry axis is marked in red.