Figure 1.

Simulated annealing F_o–F_c omit maps contoured at 3.5 σ showing ADP (to the left) and His-122 (to the right). (A) AlF₃ omit map at 2.0-Å resolution. Al³⁺ (green) in trigonal bipyramidal configuration is shown coordinating to three equatorial fluorines (orange) and with partial bonds to ADP O₇ and to His-122 Nδ. Mg²⁺ (white) has an octahedral geometry, with a tridendate coordination to the α- and β-phosphates and a fluorine atom and three water molecules (red) as additional ligands. (B) BeF₃⁻ omit map at 2.3-Å resolution. Be²⁺ (green) is modeled in a tetrahedral geometry, with three fluorines and O₇ as the fourth ligand. An alternative configuration for Be²⁺ has His-122 Nδ as the fourth ligand.