Comparison between measured and calculated ionised concentrations in Mg ²⁺/ATP, Mg ²⁺/EDTA an

Illustrations

Figure 1 A) Plot of K_app for the binding of Mg²⁺ to ATP as a function of pH_a. The fit of equation (1) at 25°C was: r = 0.99566.At 37°C the fit was: r = 0.99767At 25°C the number of experiments at each pH_a was, pH_a 5.5, 6; pH_a 6.0, 6; pH_a 6.7, 4; pH_a 7.2, 13; pH_a 7.7, 4; pH_a 8.0, 3; pH_a 8.5, 3. At 37°C, pH_a 5.36, 3; pH_a 5.50, 3; pH_a 5.90, 4; pH_a 6.7, 3; pH_a 7.2, 4; pH_a 7.7; 4; pH_a 7.9, 3; pH_a 8.2, 2.B) Plot of K_app as a function of ionic strength. The number of measurements at an ionic strength of 0.087 M was 3, at 0.156 M, 13 and at 0.3 M, 3. The filled circles are the mean values at the corresponding ionic strength. The linear regression line through the points was:K_app = -10.222 + 800.1209*Γ/2, where Γ/2 is the ionic strength: r = 0.966168.

Figure 2 A) Plot of pK_app for Mg²⁺ binding to EDTA at 25°C. The measurements have been fitted using equation : r = 0.999746.The number of measurements at pH_a 5.5 was 2; pH_a 6, 2; pH_a 6.7, 5; pH_a 7.2, 22; pH_a 7.7, 5.B) Change in the ratio R_E/T as pK_app is varied from 1.5 to 10 for pK_app values of ± 0.04, ±0.02 and ±0.01.

Figure 3 A) Calculated [Mg²⁺] in ATP buffer solutions. Filled circles are the measured concentrations; a, constants of [13] with K⁺ binding; b, constants of [11] with K⁺ binding; c, program Chelator [15] no K⁺ binding; d, [13] no K⁺ binding; e, program Maxchelator [16] no K⁺ binding; f, [11] no K⁺ binding.B) Calculated [Mg²⁺] as the ionic strength is varied from 0.06 M to 0.3 M. The [Mg²⁺] calculated using the data in figure 1B is shown as the dashed line; a, constants of [13] with K⁺ binding; b, computer program Maxchelator [16] with K⁺ binding; c, constants of [11] with K⁺ binding; d, constants of [13] no K⁺ binding; e, computer program Chelator [15] no K⁺ binding; f, constants from [11] no K⁺ binding; g, computer program Maxchelator [16] no K⁺ binding.

Figure 4 A) Calculated [Mg²⁺] in EDTA buffer solutions. Filled circles are the measured concentrations; a, computer program Chelator [15]; b, constants from [11]; c, d, constants from [12] but H⁺ ion activity calculated using the Davies equation [18] c or from [16] d; e, computer program Maxchelator [16].B) Calculated [Ca²⁺] in EGTA buffer solutions. Filled circles are the measured concentrations: a, computer program Chelator [15]; b, constants from [11]; c, constants from [14]; d, computer program Maxchelator [16] and computer program from [17] (points overlap); e, f, constants from [12] but H⁺ ion activity calculated using the Davies equation [18] e or from [19] f; g, computer program from [17] but assuming 100% purity for EGTA.