Table 2. Calculated Contributions from Specific Residues to the Electric Field along the CN Bond for the L54C-CN ecDHFR Mutant in the Closed and Occluded Conformations.

	ECN,a MV/cm		ΔECNb, MV/cm
residue	closed (NADP+/FOL)	occluded (NADP+//THF)	shift
Phe31	–0.28	0.03	0.31
Thr35	–0.75	0.60	1.35
Val40	0.16	–2.11	−2.27
Met42	0.33	–0.65	−0.98
Arg57	0.80	–5.78	−6.58
Ile94	0.33	–0.71	−1.04
FOL	–13.21	–11.27	1.95

^aComponent of the electric field along the CN bond.

^bChanges in the electric field along the CN bond in going from the closed conformation (NADP⁺/FOL) to the occluded conformation (NADP⁺/THF).