TABLE 2.

Number of protons linked to the binding of paromomycin to the E. coli 16 S rRNA A-site model oligonucleotide at pH 6.8

Buffer (10 mM)	ΔHion* (kcal/mol)	ΔHobs† (kcal/mol)	ΔHint‡ (kcal/mol)	Δndrug‡	fdrug§ (Sulfate salt)	fdrug§ (Free base)
Cacodylate	−0.47	−12.5 ± 0.1	−12.1 ± 0.1	0.88 ± 0.03	0.43 ± 0.01	0.83 ± 0.03
TES	+7.83	−5.2 ± 0.1

^*Ionization heats (ΔH_ion) at 25°C for the indicated buffers were taken from Fukada and Takahashi (52).

^†ΔH_obs values were derived from fits of the ITC profiles shown in Fig. 6 C, with the indicated uncertainties reflecting the standard deviations of the experimental data from the fitted curves.

^‡Values of ΔH_int and Δn_drug were determined using Eqs. 6a and 6b, with the indicated uncertainties reflecting the maximum errors in ΔH_obs as propagated through these equations.

^§Values of f_drug were calculated from the ¹⁵N NMR-derived pK_a values for the sulfate salt and free base forms of paromomycin using the Henderson-Hasselbalch relationship: In this relationship, is the pK_a value for the jth amino group. The indicated uncertainties in f_drug reflect the maximum errors in the NMR-derived pK_a values as propagated through the above relationship.