Table 2.

Impact of change in protein or substrate structure on the exponent that relates the H/T and D/T secondary isotope effects in the alcohol dehydrogenase reaction.

enzymea	α-2° kH/kTb	α-2° kD/kTb	EXPc	references
YADH, WT (p-H)d	1.35 (0.015)	1.03 (0.006)	10.2 (2.4)	Cha et al. (1989)
YADH, WT (p-Cl)d	1.34 (0.01)	1.03 (0.010)	9.9 (4.2)	Rucker et al. (1992)
HLADH, L57F	1.318 (0.007)	1.033 (0.004)	8.5 (1)	Bahnson et al. (1993)
HLADH, F93W	1.333 (0.004)	1.048 (0.004)	6.3 (0.5)	Bahnson et al. (1993)
HLADH, V203A	1.316 (0.006)	1.058 (0.004)	4.9 (0.3)	Bahnson et al. (1997)
HLADH, L57V	1.332 (0.003)	1.065 (0.011)	4.55 (0.75)	Bahnson et al. (1993)
HLADH, V203L	1.38 (0.005)	1.074 (0.004)	4.5 (0.2)	Bahnson et al. (1997)
HLADH, WTe	1.335 (0.003)	1.073 (0.008)	4.1 (0.44)	Bahnson et al. (1993)
HLADH, ESEe	1.332 (0.004)	1.075 (0.003)	3.96 (0.16)	Bahnson et al. (1993)
HLADH, V203A:F93W	1.325 (0.004)	1.075 (0.004)	3.9 (0.2)	Bahnson et al. (1997)
HLADH, V203G	1.358 (0.007)	1.097 (0.007)	3.3 (0.2)	Bahnson et al. (1997)
YADH WT (p-MeO)d	1.34 (0.04)	1.12 (0.02)	2.78 (0.82)	Rucker et al. (1992)

^aHLADH is horse liver alcohol dehydrogenase and YADH is yeast alcohol dehydrogenase.

^bReported values±the standard errors.

^cThe error was calculated as follows: $\text{error}=\text{exp}{\left[{\{\delta \text{ln}(k_{\text{H}}/k_{\text{T}})/\text{ln}(k_{\text{H}}/k_{\text{T}})\}}^2+{\{\delta \text{ln}(k_{\text{D}}/k_{\text{T}})/\text{ln}(k_{\text{D}}/k_{\text{T}})\}}^2\right]}^{1/2}$.

^dThese experiments used benzyl alcohols with either H, Cl or MeO substituents in the para-position of the ring.

^eH-transfer may not be fully rate-determining for these two enzyme forms, leading to a somewhat reduced value for EXP.