Table 1.

Calculated and Observed Activation Free Energies (kcal/mol) for Different Systems^a

system	ΔG‡cal	ΔG‡obs
KE07 (wt, PDB: 2RKX)	19.8	20.1
R6 3/7 F (PDB: 3IIP)	17.7	17.8
HG3 (PDB: 3NYD, S265T	15.9	16.9
HG3.17 (PDB: 4BS0)	13.8	13.7
HG3.3b	16.1	16.0
HG3.7	14.6	14.2
water (cage)	22.3	21.2

^aOur activation barriers that are evaluated (as in all of our previous works (e.g., see ref 18)) are referred to the chemical barriers. Namely, the barrier that corresponds to k_cat in the enzyme and k_cage in water. The observed result for k_cage is taken when the format ion is used rather than when acetate ion was used as a base (extrapolation of the concentration to 55M). This point is discussed in detail in ref 18.