TABLE 2.

Gibbs free energies of substrates interacting with the LmexNBT1 transporter^a

Substrate	ΔG° (kJ/mol)	δ(ΔG°) (kJ/mol)	Control
Hypoxanthine	−34.4
Adenine	−31.9	2.5	HX
Allopurinol	−26.2	8.2	HX
Aminopurinol	−22.3	9.6	Adenine
Xanthine	−28.9	5.5	HX
Guanine	−34.2	0.2	HX
Inosine	−20.3	14.1	HX
Adenosine	−17.9	14.0	Adenine
Guanosine	−21.9	12.3	Guanine
Purine	−32.5	−0.6	Adenine
1-Deazapurine	−25.3	7.2	Purine
3-Deazaguanine	−23.0	11.2	Guanine
6-Thioguanine	−29.7	4.5	Guanine
7-Deazaguanine	>−18	16.2	Guanine
9-Deazaguanine	−21.9	12.3	Guanine

^aThe Gibbs free energy of substrate-transporter interaction was calculated from the K_m and K_i values listed in Table 1, using the Nernst equation as described previously (19,58). The difference between the value and that with a control compound (either hypoxanthine [HX] as the highest-affinity compound, the corresponding physiological nucleobase [in the case of chemical analogues], or the corresponding nucleobase [in the case of nucleosides]) yielded the δ(ΔG°), the loss in binding energy relative to the control compound.