Fig. 2: Unifying model proposed by Wieruszekska, Pwlowicz et al. to explain the effect of different metal ion on Dz’s structure and activity.

According to this model the DNA’s catalytic capability is associated with at least two metal ion binding sides (MBS I and II). Binding in MBS I will induce a condensed state. (Additional) binding in MBS II will promote the cleavage reaction itself. Different metal ions will have differential affinities to the two MBSs (indicated by molarity values in parenthesis). Among the tested metal ions, Pb²⁺ has by far the highest affinity for MBS II. As a consequence, the presence of Pb²⁺ will directly promote cleavage without considerably increasing the population of the condensed (activated) state.