Table 1. Comparative Kinetic Parameters from Arrhenius Plot and Single Turnover Rates of Distal Mutants and Wild Type E. coli DHFR.

DHFR	khyd(S-1)a	kwt/kmut	AH/ATb	ΔEa(T-H)b (kcal/mol)	ΔΔEa(T-H)c
WT	228 ± 8d		7.0 ± 1.5d	–0.1 ± 0.2d
W133F	88 ± 1	3 ± 0.1	5.8 ± 0.8	–0.01 ± 0.08
G121V	1.4 ± 0.2e	163 ± 24	7.4 ± 1.6e	0.23 ± 0.03e
M42W	5.6 ± 0.4f	41 ± 3	2.8 ± 0.2f	0.58 ± 0.04f
F125M	5.44 ± 0.03	42 ± 2	1.9 ± 0.3	0.96 ± 0.09
G121V-F125M	3.76 ± 0.04	61 ± 2	0.03 ± 0.004	3.4 ± 0.1	2.2 ± 0.1
M42W-G121V	0.03 ± 0.01g	7600 ± 1300	0.1 ± 0.1g	3.6 ± 0.3g	2.8 ± 0.3
M42W-F125M	0.45 ± 0.02	512 ± 31	0.01 ± 0.003	4.0 ± 0.2	2.5 ± 0.4

^aPre-steady-state rates of H transfer at 25 °C and pH 7.

^bSimilar trends were observed for H/D and D/T (data not shown).

^cΔΔE_a(T-H) = ΔE_{a(T-H)mutant1–2} – (ΔE_{a(T-H)mutant1} + ΔE_{a(T-H)mutant2}).

^dReference (30)

^eReference (29).

^fReference (28).

^gReference (25).