Table 2. Kinetic Parameters at 25 °C for Deuterium Exchange Reactions of FUMP Catalyzed by Q215A Variant ScOMPDC at Several pD^a.

	Q215A ScOMPDCb,c			wild type ScOMPDCb
pDd	kex (s–1)	Kd (mM)	kex/Kd (M–1 s–1)	kex (s–1)	Kd (mM)	kex/Kd (M–1 s–1)	ΔΔG‡e kcal/mol
7.1 (7.03)	(2.7 ± 0.1) × 10–4	2.0 ± 0.2	0.13	1.7 × 10–2	0.51	33	3.3
7.4 (7.37)	(3.6 ± 0.1) × 10–4	0.70 ± 0.08	0.51	2.4 × 10–2	0.17	140	3.3
7.7 (7.64)	(4.1 ± 0.08) × 10–4	0.38 ± 0.04	1.08	3.2 × 10–2	0.11	300	3.3
8.1 (8.15)	(4.3 ± 0.08) × 10–4	0.42 ± 0.03	1.02	4.4 × 10–2	0.11	400	3.5
9.3 (9.33)	(3.0 ± 0.1) × 10–4	0.54 ± 0.03	0.56	3.8 × 10–2	0.19	200	3.6

^aFor ScOMPDC-catalyzed deuterium exchange reactions at I = 0.1 (NaCl) at: pD 7.1, 50 mM imidazole buffer; pD 7.4. 50 mM MOPS buffer; pD 7.7, 50 mM MOPS buffer; pD 8.1, 50 mM GlyGly buffer; and, pD 9.3, 50 mM GlyGly buffer.

^bKinetic parameters defined by Scheme 2.

^cThe uncertainty in these values is the standard error from the least-squares fit of the kinetic data to the appropriate kinetic equation.

^dThe pDs in parentheses for the previous study on the wild type ScOMPDC-catalyzed deuterium exchange reaction were reported to three significant figures.⁶

^eThe effect of the point substitution on the activation barrier ΔG^‡ for k_ex/K_d.