TABLE 1.

Estimated standard free energy for ATP hydrolysis

pHC	8.5	7.5	6.0	5.0
Free Mg2+/mM	0.28	0.33	0.94	2.50
Free Mg-ATP/mM	3.2	3.3	2.95	1.85
−ΔG0 (KJ/mol)	45.2	39.8	36.0	36.2
KATP (106 M)	83.8	9.47	2.04	2.21

Values calculated for ATP medium, containing 125 mM KCl, 5 mM MgCl₂, 5 mM K₂-ATP, 5 mM K-ADP, 10 mM KH₂PO₄, 0.5 mM EGTA, and 5 mM MES titrated to the given pH with Tris base; calculated ionic strength was ∼0.2 M. Free Mg²⁺ and Mg-ATP concentrations were obtained via the algorithm calcium.exe (Ver. 2.1), developed by Föhr et al. (1993). ΔG₀ values were extracted from Alberty (1968).