Table 6.

Heats of formation used in estimating the change in energy of the hydrogen bonds in the oxyanion site

System	Description	ΔHf (kcal mol−1)†
H(A)	Step 1 unmodified	0.00
H(B)	Step 2 unmodified	−2.54
X(A)	Step 1 with -NH on Gly193 replaced with -O	−32.35
X(B)	Step 2 with -NH on Gly193 replaced with -O	−21.29
X(A)	Step 1 with -NH on Ser195 replaced with -O	−26.56
X(B)	Step 2 with -NH on Ser195 replaced with -O	−15.84
X(A)	Step 1 with -OH on Thr253 replaced with -F	+6.97
X(B)	Step 2 with -OH on Thr253 replaced with -F	+11.56

†: All heats relative to step 1 un-modified system