Figure 9.

Correlation between [Mg²⁺]_1/2 values for individual pyrene-labeled P4-P6 derivatives as determined by native gels and by fluorescence. The diagonal line has a slope of exactly 1.0. Each of the 12 data points in the plot represents a different combination of pyrene site and tether. Wild-type P4-P6 without an attached pyrene has [Mg²⁺]_1/2 of 0.64 mM in this set of experiments. The native gel [Mg²⁺]_1/2 values represented in this plot correspond to ΔΔG°′ values between ∼0.3 and ∼6 kcal/mol (see Supplementary Data for tabulation of data). Values of [Mg²⁺]_1/2 are reproducible with <5% error between independent determinations. Because ΔG°′ = nRT•ln[Mg²⁺]_1/2, where n is the Mg²⁺ Hill coefficient (16,28), the [Mg²⁺]_1/2 values are plotted on logarithmic axes.