Table 1.

Comparative KIEs on Arrhenius preexponential factors

Parameters	DHFR				S.C. range (46,49,51)
	WT (35)	G121V (41)	M42W (44)	G121V–M42W (This work)
kH*	228 ± 8 s−1	1.4 ± 0.2 s−1	5.6 ± 0.4 s−1	0.03 ± 0.005 s−1
AH/AT	7.0 ± 1.5	7.4 ± 1.6	2.8 ± 0.2	0.1 ± 0.1	0.5–1.6
AH/AD	3.5 ± 0.5	4.7 ± 1.5	2.1 ± 0.2	0.04 ± 0.03	0.6–1.4
AD/AT	1.70 ± 0.14	1.7 ± 0.07	1.35 ± 0.05	0.25 ± 0.09	0.9–1.2
ΔEaT-H†, kcal/mol	−0.1 ± 0.2	0.23 ± 0.03	0.58 ± 0.04	3.6 ± 0.3

*Presteady state rates of H transfer at 25 °C and pH 7 (33)

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