It is already well accepted that a deprotonated Tyr can serve as a proton acceptor residue in enzymatic reactions. However, for Tyr to be in its deprotonated state, its pKa must be lower than the pH of the experimental condition, which typically ranges between 7.5-8. We note that the pKa of the Tyr side chain is ~10.1 ; nevertheless, prior study has shown that an increased hydrogen bonding network near Tyr lowers its pKa. Similarly, a recent experiment demonstrates that replacing Tyr with FluoroTyr results in a significant alteration of the pKa (lowering to ~6.5). This change is also attributed to modifications in the hydrogen bonding interactions near Tyr.