TABLE 1.

Thermodynamic parameters of A-site binding of pept-tRNA^a

pept-tRNA	ΔH° (kcal/mole)	ΔG° (kcal/mole)	ΔS° (cal/mole/°K)	TΔS° (kcal/mole)
Y37 (10 mM Mg2+)b	−47 ± 4	−10.0 ± 0.3	−120 ± 11	−37 ± 4
Y37 (6 mM Mg2+)	−47 ± 4	−8.5 ± 0.3	−125 ± 11	−39 ± 4
Y37G	−47 ± 6	−6.9 ± 0.3	−128 ± 19	−40 ± 6
Y37A	−42 ± 2	−8.6 ± 0.1	−107 ± 6	−33 ± 2
Y37U	−15 ± 2	−8.2 ± 0.1	−21 ± 6	−7 ± 2
Y37C	−15 ± 1	−8.1 ± 0.1	−22 ± 4	−7 ± 1
−Y (20 mM Mg2+)	−14 ± 1	−8.6 ± 0.1	−15 ± 2	−5 ± 1
−Y (10 mM Mg2+)b	−14 ± 1	−7.4 ± 0.1	−19 ± 2	−6 ± 1

^aΔG° values were calculated from K_d values measured at 310°K according to the equation ΔG° = RTlnK_d; ΔH° and ΔS° values were determined from the slope and the Y-axis intercept of the log(K_d) versus 1/T plot, respectively (Fig. 3C ▶).

^bExtrapolated on the basis of the linear Mg²⁺ dependence of the respective K_d values (Fig. 5 ▶).