Examples of bound betaine and sarcosine molecules. The color scheme is identical to that in Fig. 6. Cyan spheres, Cl− ions. Large sticks, betaine. Small sticks, sarcosine. The maps show OMIT DELFWT/PHDELFWT electron density from REFMAC contoured at +3σ/−3σ (cyan/red) (Murshudov et al., 2011). The maps were calculated after restrained refinement of the initial model with water molecules in the vicinity of the ligands removed but before building betaine molecules into the model. (a, c) Two examples from tetragonal thermolysin at 2.00 Å resolution (betaine) and 2.10 Å resolution (sarcosine). (b, d) Two examples from orthorhombic trypsin at 1.95 Å resolution (betaine) and 1.70 Å resolution (sarcosine). This figure was prepared with PyMOL (Schrödinger LLC).