Fig. 2.

The calculated product states of the 82-atom system are shown for both RC (PDB entry 1ATP) and TC (PDB entry 1L3R). The TC structure has a lower barrier than the RC structure and a favorable product state because in the product and transition states the central Mg atom can remain octahedrally coordinated. In the RC conformer the reaction cleft is opened and the same Mg atom is forced to break one bond, making the reaction unfavorable. The distance between the coordinating oxygen atoms on the Asn-171 and ADP groups, which is a measure of reaction center size, is increased from 4.2 Å in the TC structure to 5.1 Å in the RC structure.