Table 1. Kinetic Parameters at pH 7.5 and 25 °C for Enzyme-Catalyzed Reactions of Whole and Phosphodianion Truncated Substrates (Scheme 2), the Total Phosphodianion Binding Energies, and the Dianion Binding Energy Utilized for Enzyme Activation.

	(kcat/Km)SPi	(kcat/Km)S		(ΔG⧧)Pi (kcal/mol),h,j	ΔGHPi⧧  (kcal/mol),i,j
enzyme	(M–1 s–1)e,f	(M–1 s–1)e,f	(M–2 s–1)f,g	[IBE]T	[IBE]HPi	[IBE]HPi/[IBE]T
ScPGIa	(6.9 ± 0.2) × 105	(3.6 ± 0.2) × 10–4	0.52 ± 0.10	12.6 ± 0.1	4.3 ± 0.1	0.34
	kcat = 400 s–1
LmG6PDHa	(2.0 ± 0.2) × 106	(8.3 ± 0.1) × 10–3	53.0 ± 0.3	11.4 ± 0.1	5.2 ± 0.1	0.46
	kcat = 320 s–1
Ec6PGDHb	(8.4 ± 0.4) × 105	(9.9 ± 0.2) × 10–3	140 ± 1	10.8 ± 0.1	5.7 ± 0.1	0.53
	kcat = 12 s–1
OMPDCc	1.1 × 107	0.026	12000	11.7 ± 0.1	7.7 ± 0.1	0.66
TIMd	2.2 × 108	0.062	2700	13.0 ± 0.1	6.3 ± 0.1	0.48
GPDHd	4.6 × 106	0.050	16000	10.8 ± 0.1	7.5 ± 0.1	0.69

^aSPi = G6P; S = d-xylose.

^bSPi = 6-PG; S = d-xylonate.

^cSPi = orotidine 5′-monophosphate (OMP); S = 1-(β-d-erythrofuranosyl)orotic acid.^6,18

^dSP_i = dihydroxyacetone phosphate; S = glycolaldehyde.^2,6

^eKinetic data for the catalyzed reactions of whole or truncated substrate (see SI).

^fThe quoted uncertainty is the standard error obtained from the least-squares fit of experimental data to the appropriate kinetic equation.

^gThird-order rate constant for the phosphite dianion-activated reaction of truncated substrate (Scheme 3).

^h(ΔG^⧧)_Pi = RT ln[(k_cat/K_m)_SPi/(k_cat/K_m)_S].

ⁱSee eq 3.

^jThe approximate uncertainties are calculated from the standard errors in the kinetic parameters.