J. Phys. Chem. B 112, p. 14729-14741 (2008)
Location of water B :
|Below are shown the
energy profiles of two proton transfers via water B.
Insets give the geometries in the reactant,
product, the rate-limiting transition states, and the local minima discussed in the paper.
The transferring protons are depicted as small spheres. The reaction coordinate L gives the sum along the entire path of the
changes in all atomic coordinates calculated as a root-mean-squared difference: At L=0, the Schiff base is protonated and Asp85 is negatively
charged; at L=1, Asp85 is protonated and the Schiff base is neutral. The energies are for QM/MM-optimized geometries.
Path 1a: Proton transfer via water B. Download the movie (1.3 Mb)
First, water B moves to a location where it bridges between the Schiff base and Asp85. Then, concerted proton transfer via water B occurs, crossing a rate-limiting barrier of 9.7 kcal/mol, which is consistent with the 10 microseconds experimental timescale of the primary proton transfer step (L to M). Finally, water B remains hydrogen-bonded to the deprotonated Schiff base.
Path 2a: Proton transfer via water B and
Download the movie
In the starting state, a hydrogen-bonded network already extends
the Schiff base to Asp85 via water molecule B and Thr89. Therefore, the
proton transfer requires only minute structural rearrangements,
crossing a rate-limiting barrier of 13.8 kcal/mol.
Go to Home of S. Fischer