Fig. 1.

The first steps of various mechanistic options for the hydrolysis of generic triphosphate monoester in solution. The red arrows correspond to the reaction coordinate, and the black dashed lines correspond to the partial bond formation/breaking. NA and PT are abbreviations for the nucleophilic attack and the proton transfer, respectively. [A represents the mechanistic option where the PT from the nucleophilic water to the phosphate oxygen occurs before the NA (1W)]. B represents the mechanism where the proton is transferred directly from the attacking water to the substrate, but NA precedes the PT step (1W′), while C denotes a two-water mechanism (2W), where the NA is the first step and a PT through a second water follows the NA. The red arrows in the products of the first steps represent the changes in the second step.