Table 1.

Comparative kinetic parameters of the DHFR I14 mutants.

Parameters	WT	I14V	I14A	I14G
Residue volumea (Å3)	124	105	67	48
kHb [s−1]	228 ±8d	33.3 ±3.1f	5.7 ±0.3f	0.22 ±0.04f
AH /AT c	7.0 ±1.5e	4.2 ±0.4f	4.7 ±0.5g	0.024 ±0.003f
ΔEaT-Hc, [kcal/mol]	−0.1 ±0.2e	0.27 ±0.05f	0.39 ±0.06g	3.31 ±0.07f

^aSide chain volume.⁵⁷

^bPresteady state rates of H transfer at 25°C and pH 7.

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

^dRef. 58.

^eRef. 47.

^fThis work.

^gRef. 46.