Figure 3.

Correlations between k_act and some physico-chemical properties of the activating divalent metal ions (represented by different symbols: Mg²⁺, open circles; Ca²⁺, closed circles; Ba²⁺, open squares; Sr²⁺, closed squares; Co²⁺, open diamonds; Mn²⁺, closed diamonds; Cd²⁺, open triangles; Ni²⁺, closed triangles; Zn²⁺, crossed circles). (A) Correlation between k_act and the pK_a of the hydrated metal ion. pK_a values were taken from Richens (47). The solid line represents a linear least-squares fit of the data, with slope = –0.76 ± 0.1 and R² = 0.87. (B) Correlation between k_act and the affinity of the metal ions for 5′AMP. The values of K_d^M·5′AMP (the dissociation constant of the metal–5′AMP complex) were obtained from Massoud and Sigel (48). The solid line represents a linear least-squares fit of the data, with slope = –2.2 ± 0.4 and R² = 0.81.