. Author manuscript; available in PMC: 2008 Sep 15.

Published in final edited form as: J Am Chem Soc. 2007 Feb 7;129(5):1312–1320. doi: 10.1021/ja066780e

Table 2.

Measured and calculated enthalpy and entropy values for intermolecular and intramolecular binding of sulfonamides to modified and unmodified HCA** proteins.

Protein	Ligand	K_d × 10⁶	ΔG^o kcal mol⁻¹	ΔH^o kcal mol⁻¹	-TΔS^o kcal mol⁻¹
HCA**	DNSA	0.30 ± 0.014^a,^b,^c	−8.90 ± 0.15	—	—
HCA**-SSEG₂CONH₂	DNSA	0.26 ± 0.008^a,^b,^c	−8.98 ± 0.10	—	—
HCA**-SCH₂CO₂⁻	DNSA	0.23 ± 0.007^a,^b,^c	−9.05 ± 0.10	—	—
	Ethox	0.0002 ± 0.00004^a,^b,^d	−13.2 ± 0.6	−17.7 ± 0.4^e,^f	+4.5 ± 0.7
	SA-OMe	0.51 ± 0.018^a,^b	−8.58 ± 0.11	—	—
	SA-OMe	0.55 ± 0.03^a,^e	−8.54 ± 0.16	−6.10 ± 0.12^e,^f	−2.4 ± 0.2
HCA**-SSEG₁₀SA	Ethox	6.1 ± 0.01^a,^e,^g	−7.12 ± 0.08	−11.0 ± 0.6^e,^f	+3.9 ± 0.6
	Intra^h	33 ± 7ⁱ	−6.1 ± 0.6	−6.7 ± 0.7^e,^f	+0.6 ± 0.9

Units of M.

Measured by fluorescence either directly or through competition with DNSA.¹⁶, ¹⁷, ²⁴, ²⁵ Uncertainties are 95% confidence intervals from curve-fitting.

Compare to literature value of 0.3 μM for the binding of DNSA to a Cys-206→Ser mutant of HCA.²²

Compare to literature value of 0.2 nM for the binding of Ethox to bovine carbonic anhydrase II.¹⁷

Measured by calorimetry.

Uncertainties were assumed to be due primarily to errors in the quantitation of titrant.³⁰ An uncertainty of 2% of ΔH^o was taken for the binding to HCA**-SCH₂CO₂⁻ and 5% of ΔH^o for the binding to HCA**-SSEG₁₀SA.

Compare to value from fluorescence of 2.4 μM (Table 2).

Thermodynamic parameters are those for the intramolecular equilibrium shown in Figure 1D.

ⁱ

Dimensionless.