Table 3.

The enthalpy changes of the interaction of E3 and E1 with PSBD in different buffers at different pH values

		E3		E1
pH	Buffer	ΔH°obs (kcal/mol)	Protons linkeda (n)	ΔH°obs (kcal/mol)	Protons linkeda (n)
5.5	cacodylate	3.9	−1.14 ± 0.14	−7.5	−0.64 ± 0.21
	MES	−1.8		−11.5
	Bistris	−4.3		−12.0
6.5	cacodylate	2.9	−0.36 ± 0.04	−9.2	0.1 ± 0.01
	MES	1.6		−8.8
	Aces	0		−8.4
7.4	cacodylate	2.0	−0.02 ± 0.05	−9.4	0.11 ± 0.08
	MES	1.6		−8.2
	Hepes	2.1		−8.5
	Aces	1.8		−8.6
8.5	Hepes	1.9	0.08 ± 0.07	−10.8	−0.02 ± 0.18
	Tricine	1.7		−9.8
	Tris-HCl	2.4		−10.8

All experiments were repeated twice and the average values are listed. The buffer conditions were 20 mM buffer, 150 mM NaCl and 3.4 mM EDTA at 25°C.

^a The number of protons exchanged upon binding was obtained from the slopes of plots of ΔH_obs versus ΔH_ion in Figure 4 ▶.