The limited role of quantum effects in proton transfer in enzymes

I am just finishing up a paper which gives a detailed analysis of the possible role of quantum effects in proton transfer in enzymes. Above I reproduce a key figure from the paper (if you left click on it, you can view a larger version)

This follows a series of posts:
the first discussed the claims that proton transfer in enzymes occurs predominantly by quantum tunneling below the transition state associated with the transition state.
the second reviewed beautiful experiments by Doll and Finke which were inconsistent with Klinman's hypothesis that enzymes have evolved to promote tunneling, and
the third post reviewed Quantum transition state theory and how instantons provide a natural description of quantum tunneling.

The Figure shows that a quantitative description of the Doll and Finke data is possible without instantons, i.e., the only quantum effects are those associated with fluctuations around the transition state.