Activation Energies of H/D Exchange
Arrhenius plots of the observed H/D exchange rates give
us the activation energy for the exchange process. Comparing the
results for G6PDH and wild-type alkaline phosphatase (WT AP) shows
that the barrier to exchange in G6PDH is significantly lower.
While the tryptophan responsible for the longest lifetime in G6PDH has
not been identified, it is clear from an examination of the crystal
structure that none of the tryptophans are as deeply buried as W109 in
AP. Thus, this observation is consistent with our belief that a local
unfolding or ëëbreathing motioníí of the protein is
required for penetration of the D2O.
Figures 3a, 3b: Comparison of the calculated activation
energies for the H/D exchange process for WT AP and G6PDH
LADH Exhibits H/D Exchange